President Trump's travel ban targeting a dozen countries went into effect on Monday, the latest step by the White House to crack down on the number of individuals entering the U.S.

The new policy fully restricts the entry into the United States of nationals from Afghanistan, Chad, the Republic of the Congo, Equatorial Guinea, Eritrea, Haiti, Iran, Libya, Myanmar, Somalia, Sudan and Yemen.

It also partially restricts entry into the U.S. for nationals coming from Burundi, Cuba, Laos, Sierra Leone, Togo, Turkmenistan and Venezuela.

The policy makes exceptions for nationals from all 19 of those countries who are lawful permanent residents of the United States or existing visa holders and individuals “whose entry serves U.S. national interests.”

The travel ban is taking effect amid rising tensions in Los Angeles around immigration raids in the city.

Trump and White House officials have argued the travel restrictions are based on national security concerns, specifically with vetting procedures involving the listed countries.

Trump’s attempts to restrict entry into the United States from certain Muslim-majority countries in his first term drew legal challenges and protests at airports across the country.

This time around, experts have suggested he is likely on firmer legal footing in part because of a Supreme Court ruling that upheld the third version of his first-term ban and in part because the administration laid the groundwork with an executive order focused on enhanced vetting.