Economically distressed areas may not benefit from a new tax perk aimed at driving in investor capital unless the IRS clarifies how the rules will apply to startups.

The first set of rules on opportunity zones (REG-115420-18) favor long-term real estate projects and don’t ensure flexibility for startup investments—the sector that will drive the job growth and economic development intended by the incentive, practitioners said. That lack of certainty could keep the tax incentive from attracting a...