European Commission President Jean-Claude Juncker in Brussels on Wednesday. (Stephanie Lecocq/European Pressphoto Agency)

A top E.U. leader warned Wednesday that a U.S. congressional vote to strip President Trump of the ability to remove sanctions against Russia could backfire, dealing a blow to transatlantic efforts to curb Russian aggression against Ukraine and sparking a trade war between Europe and the United States.

The House of Representatives approved the measure Tuesday, 419 to 3, after the Senate passed similar legislation last month in a 98-to-2 vote. The White House has not indicated whether Trump will sign the bill.

The bill’s main goal is to force Trump to consult with Congress before dialing back sanctions, a reaction to a White House plan weighed in his first weeks in office to unilaterally end the measures against the Kremlin. But the legislation would also give Trump the power to ban investments in certain Russian energy projects, most notably a major Russia-to-Germany gas pipeline under development called Nord Stream 2, and to promote U.S. energy exports instead.

The legislation’s language was softened in the days ahead of the vote, in apparent acknowledgment of European worries. But many policymakers and experts in the European Union’s capital, Brussels, and in Berlin still say that Congress may ultimately harm its own effort to pressure Russia. The worries are also a measure of the Trump White House’s diminished standing in Europe, since the policymakers are mistrustful of U.S. natural-gas exports that were welcomed during the Obama administration.

“The U.S. bill could have unintended unilateral effects that impact the E.U.’s energy security interests,” European Commission President Jean-Claude Juncker said in a statement Wednesday. “If our concerns are not taken into account sufficiently, we stand ready to act appropriately within a matter of days. America first cannot mean that Europe's interests come last.”

(U.S. House of Representatives)

Separately, the German government questioned the move, voicing suspicions that the measure may simply be an effort to boost U.S. energy exports by hammering European gas projects.

It is “unacceptable for the United States to use possible sanctions as an instrument to serve the interests of U.S. industrial policy,” German Foreign Ministry spokesman Martin Schaefer said in Berlin.

The initial U.S. sanctions on Russia after its 2014 annexation of Ukraine’s Crimean Peninsula were unusual because they were negotiated with the E.U. Obama administration policymakers reasoned that their efforts would have a bigger effect if they presented a united front with Europe, which carries on far more trade with Russia than does the United States. Since then, policymakers on both sides of the Atlantic have moved largely in lockstep.

But Trump’s unusual friendliness with Russian President Vladimir Putin raised concerns about whether he would abandon the E.U. on sanctions, and Congress responded with near-unanimity to strengthen the measures.

The bill also gives Trump the power to impose sanctions on the pipeline under development between Russia and Germany, a project that many policymakers in Europe and the United States say will harm Ukraine by enabling Russian gas to completely bypass it. The pipeline — which will double the capacity of the existing Nord Stream link — may also increase European dependence on Russian gas imports.

Days ahead of the vote, language was added to the bill saying that the president should coordinate with U.S. allies before moving on this front, in what backers view as an attempt to calm European concerns.

“I think what we have done is made them comfortable,” said Sen. Bob Corker (R-Tenn.), who is chairman of the Senate Foreign Relations Committee and helped spearhead the legislation.

Many in Eastern Europe are wary of the pipeline project and welcome any effort to quash it. But even some European critics of the pipeline say that the U.S. push is counterproductive and that Europe would be better off fighting Nord Stream internally and on its own terms.

“They are making more enemies from this anti-Nord Stream policy than they needed to,” said Georg Zachmann, an energy expert at Bruegel, a Brussels-based think tank. “Essentially, if it’s not managing to kill the project, it’s strengthening it.”

That was underlined in a joint declaration of support for the pipeline project from the German foreign minister and the Austrian chancellor last month.

Because the sanctions measure also declares support for “the export of United States energy resources in order to create American jobs,” alarm bells have sounded in Europe that the bill is targeting Nord Stream simply so that U.S. industry can prosper. The Obama administration also fought the pipeline and opened U.S. natural gas for export, but it did so as part of a more cooperative approach with Europe.

“You have all of the narrative behind it, of America first,” said Kirsten Westphal, an energy security expert at the Berlin-based German Institute for International and Security Affairs. “President Trump is complaining about the high exports of Germany — if you change the terms of trade in a sense, and if you make Germany import more expensive LNG [liquefied natural gas] from somewhere, maybe the U.S., then this would also alter the broader balance of trade. The Europeans see the broader picture.”

U.S. defenders of the effort to limit Trump’s ability to roll back sanctions say Europe should calm its concerns.

“We didn’t set out to fight with the European Union. We set out to counter Russia,” said Daniel Fried, who directed the Obama administration’s sanctions policies until January. “This bill was not directed against Europe by the Trump administration. It was directed against the Trump administration by both parties in Congress.”

Karoun Demirjian in Washington contributed to this report.