The U.S. will investigate a French plan to impose taxes on technology companies, a move that has been a prelude to new U.S. tariffs under the Trump administration.

U.S. Trade Representative Robert Lighthizer will have as long as a year to examine whether the plan would hurt U.S. technology firms, and suggest remedies. The so-called 301 investigation is the same tool President Donald Trump used to impose tariffs on Chinese goods because of the country’s alleged theft of intellectual property.

“The United States is very concerned that the digital services tax which is expected to pass the French Senate tomorrow...