European diplomats drew a line in the sand this month, telling U.S. officials their bullying tactics wouldn’t help marshal support for President Donald Trump’s Iran policy.

The firm response came in a conference call in early January when a senior State Department official threatened European car makers would be hit with tariffs unless the European Union backed Trump’s hard line. Diplomats from Germany, France and the U.K. said that such tactics were completely unacceptable and would not help the president achieve his goals, according to U.S. and European officials familiar with the exchange.

The State Department team was struck by the firmness of the European line and passed their message on to the White House and officials from both sides noted the the U.S. administration dialed back the pressure on its European allies in the days that followed.