The U.S. announced on January 21 that it has begun implementing new visa regulations under which European Union citizens who are dual nationals of Iran, Iraq, Syria, or Sudan, or who have traveled to those countries since March 2011, need to apply for a visa.
The new rules include some limited exceptions for those who have visited the targeted countries as journalists, during government duty, official humanitarian work, and legitimate business purposes.
State Department spokesman Mark Toner said waivers and exemptions would be applied "on a case-by-case basis."
The changes to the visa-waiver program, passed by the U.S. Congress in December and signed into law by U.S. President Barack Obama, have been criticized by civil rights groups and others as discriminatory.
"It is wrong and un-American to punish groups without reason solely based on their nationality, national origin, religion, gender, or other protected grounds," the American Civil Liberties Union said in a letter in December.
The restrictions were passed in the wake of terrorist attacks in Paris and San Bernardino, California.
U.S. officials have said the changes are designed to keep the United States safe from terrorist attacks.