Diplomats from the 28-member European Union have warned Washington there could be a reciprocal response if it implements measures making it more difficult for EU citizens to enter the United States.
EU Ambassador to the United States David O'Sullivan wrote in the Washington political journal The Hill on December 14 that U.S. plans to begin biometric checks for some EU citizens "would represent the de facto introduction of a visa regime in all but name."
O'Sullivan was writing on behalf of the 28 EU member-state ambassadors to the United States.
His letter came one week after the U.S. House of Representatives voted in favor of a bill that would toughen entry into the United States for EU citizens and bar anyone who traveled to Iraq, Syria, Iran, or Sudan after March 1, 2011.
The White House supports the legislation, which was inspired by the November 13 terror attacks in Paris that killed 130 people.
O'Sullivan said the bill would institute "indiscriminate action" against the some 13 million European citizens who come to the United States every year and could trigger reciprocal measures against U.S. citizens coming to EU countries.