Washington (CNN)The U.S. began implementing changes Thursday to its visa policies that will make it harder for some Europeans to travel to the United States in a bid to keep ISIS adherents out of the country.

The new rules apply to European, Japanese and Australian travelers to the United States who have visited Iran, Iraq, Sudan or Syria since 2011 and dual-citizens who have citizenship in one of those countries.

Under the change, these individuals will no longer be able to enter the United States without applying for a travel visa.

Currently, the Visa Waiver Program allows citizens of participating countries to travel to the U.S. without obtaining a visa. Thirty-one of the 38 countries in the program are European nations, with some Asian countries included as well, according to the State Department.

The adjustment was mandated by legislation passed in the wake of November’s deadly ISIS-linked terrorist attacks in Paris, where several of the perpetrators were European citizens.