The world’s biggest tech companies are staring down the barrel of a new tax on their European revenue.

The EU’s divisive effort to create a special tax for Google, Facebook, and their peers is at a pivotal moment as proponents of the so-called digital tax push for a December vote. The measure would impose a 3 percent temporary turnover tax on the biggest multinational tech companies—those with 750 million euros or more in global turnover and 50 million euros in EU sales.

The tax is more than just a new levy. It could create deep fissures in the global consensus on how to tax major companies.

The companies it would hit hate the measure, which would take a bite out of their European revenue and could tax them twice on the same income. They have a champion in the U.S. government, which is pushing back on the measure because it singles out only digital, and mostly American, companies.

Austria, the current leader of the EU, hopes to get all member states on board before EU economics and finance ministers meet again on Dec. 4, which means winning over countries like Ireland that have staunchly opposed it. If the tax doesn’t pass by the end of the year they may lose their chance, as the EU presidency changes hands in January and Europe holds parliamentary elections in 2019.

Meanwhile, the Organization for Economic Cooperation and Development is working on a digital tax solution of its own. Some countries are urging the EU to wait until the OECD produces a proposal all its members agree on, but that could take until 2020, and some EU members are eager to act soon.

Here’s what could happen next.

The EU could vote to enact the digital services tax.

The proposed tax is meant to solve years of complaints from a group of politicians, commentators, and corporate watchdogs in Europe. They contend the business model of digital companies allows them to more easily take advantage of low tax rates around the world. Digital companies are also able to profit from selling or advertising to consumers in other countries without paying the same taxes their domestic counterparts face, the proponents say.

The tax would cover targeted online advertising sales as well as the revenue generated on commissions by platforms that connect service buyers and sellers, like vacation home rental sites or the Marketplace portion of Amazon’s business, which lets consumers buy items from third-party sellers.

Tech companies are hoping it doesn’t happen.

The proposal would tax revenue rather than profits, a departure from the way corporations are currently taxed, and could create “a massive double taxation issue” and a complex compliance burden, said Jennifer McCloskey, vice president of policy at the Information Technology Industry Council, which represents the global tech industry.

“You could theoretically turn a profitable company into a loss company” if its margin is under 3 percent, said John Warner, shareholder at Buchanan Ingersoll & Rooney PC in Washington. Many of the largest tech companies are likely to have higher margins, but not all of them. For example, every year since 2014, Amazon has reported a net operating loss outside of North America, spending more than it earned.

The revenue hit to any company could still be significant.

“A 3 percent tax on gross may be a lot higher than a 21 percent tax on net, depending on what your margin is,” Warner said.

Companies faced with the additional tax cost might pass it on to their customers, treating it as they would a tariff, said Brett Weaver, an international tax partner with KPMG LLP.

The tax could even be significant enough to change a company’s decision to do business in Europe, according to a person who works for one of the companies that would be affected and asked not to be named. The extra tax could distort the market, encouraging people to invest elsewhere and then sell into Europe so they’re not subject to the tax, this person said.

Companies are also concerned about the amount of consumer data they’d have to track and save in order to determine their tax liability in each jurisdiction, particularly following EU enactment of the far-reaching General Data Protection Regulation in May.

Compliance is “going to be a big issue from what we’ve seen so far,” for some companies, if the draft version of the measure passes, Weaver said.

The measure’s fate currently rests with Germany, which appears to be getting nervous about passing a tax that could hit some of its own large companies and could anger the U.S., potentially triggering retaliatory tariffs.

The OECD could answer the questions at the center of the debate in a way that satisfies all its members.

That won’t be easy. Countries don’t even agree on the problem. Are they trying to redefine when a digital company has a permanent establishment, or taxable business presence, in a jurisdiction? Are they reevaluating what kinds of economic activity create value for a company—such as selling user data—and how to tax it? Or just making sure the largest companies pay their fair share of taxes?

Divides on the digital tax could lead to deeper rifts if countries come to disagree about the fundamentals of global corporate taxation—which country has the right to tax a company, for instance.

“I think the bigger risk to the international tax order is that these issues won’t be resolved,” Warner said. That could start to unravel the international progress on tax harmonization made over the last 50 years, “and that’s a bit of apocalyptic territory,” he added.

The companies at the center of the debate would be happy if Europe dropped the digital tax and adopted almost any long-term solution the OECD came up with that met a few criteria, Weaver said.

“That it doesn’t ring-fence any sector of the global economy, so all are treated fairly and the same. That it’s not a transactional tax or a tax on revenue, but rather continues to tax companies on their profits. And lastly, that it’s not a system that has a lot of concerns around double taxation and controversy.”

The OECD remains optimistic.

“What is clear to me is that there is appetite, I would think, for a broad approach which would be a global approach at the OECD level to go beyond digital and try to finish the BEPS work,” Pascal Saint-Amans, the director of the OECD’s Center for Tax Policy, told Bloomberg Tax, referring to the organization’s project to tackle base erosion and profit shifting.

The EU could pass its digital tax, then undo it if the OECD lands on a satisfactory solution.

Companies, along with the U.S. government, are hoping the EU pauses its efforts to allow the Organization for Economic Cooperation and Development to produce a global solution by its 2020 deadline.

EU lawmakers are considering a sunset clause that could unwind the temporary law if the OECD reaches its own consensus solution, or commit EU leaders to reviewing their measure in light of further OECD action, according to confidential EU documents obtained by Bloomberg News in October. An official later confirmed that.

“All members are clear that the short-term interim solution of a digital service tax has to end when there is a global solution on the basis of OECD,” Hartwig Loeger, the Austrian finance minister, said Nov. 6 in public remarks at a meeting of the European Economic and Financial Affairs Council.

This outcome would please companies concerned about the digital tax—if the tax really is cut off, which some of its critics doubt will happen. In an October letter to European leadership urging the EU to abandon the proposal, top U.S. Senate tax writers worried it could last indefinitely.

Even if the EU fails to pass the digital services tax, individual countries could move forward with their own versions.

If the tax doesn’t pass, tech giants might face an even worse alternative: individual countries passing slightly different versions of a similar digital tax.

“That’s also a really bad scenario,” McCloskey said.

Unilateral actions would create a “patchwork of very hard to administer policies” around the world, McCloskey said, and laws enacted by some countries could inspire others.

“You could have this contagion of policies, but they’re not all in line,” McCloskey said.

The U.K. just introduced a 2 percent turnover levy on digital services, and countries including Italy and Spain are also moving forward with implementing their own versions of a digital tax. The EU has cited unilateral actions like these as justification for pushing ahead with its own proposal before the OECD reaches a solution, saying that EU-wide action is better than individual actions by member states.

The solution could answer an entirely different question.

The digital tax debate took a surprising turn earlier this year when Olaf Scholz, Germany’s finance minister, started calling for a global minimum tax. Scholz hasn’t provided much detail, but a U.S. Treasury official thinks the plan could create something like the measures the U.S. enacted in its 2017 tax legislation, effectively imposing a minimum rate of tax on a multinational’s foreign entities.

Or Scholz’s statements might be political theater: Germany trying to avoid angering the U.S. by appearing to back away from the digital tax without fully renouncing an idea that’s politically popular with its own electorate, said Matthias Bauer, a senior economist at the European Centre for International Political Economy.

Meanwhile, German companies are urging the EU to abandon the proposal, which “leads to double taxation of companies and harms German industry,” the Federation of German Industries said in a September paper.

The German proposal doesn’t address the digital questions but a different, familiar problem: the concern over multinationals achieving “stateless income” by moving valuable intellectual property to very low-tax jurisdictions that originally catalyzed the OECD’s efforts to tackle base erosion and profit shifting five years ago.

“If you put all these pieces together, you have a question which has not been solved, and remains a big question facing the tax challenges of the digitalization of the economy, the future of the economy, the future of the international tax system,” Saint-Amans told Bloomberg Tax. “We did BEPS, then we did the implementation of BEPS. Now I think there is reflection on what could be next.”