A scaled back version of Donald Trump's travel ban on citizens from several Muslim-majority countries has come into effect.
People from six countries, as well as all refugees, will now face a much more rigorous procedure to gain entry to the US.
Under the temporary rules, citizens of Syria, Sudan, Somalia, Libya, Iran and Yemen who already have visas will be allowed into the United States.
But people from those countries applying for new visas will now have to prove a close family relationship or an existing relationship with an entity like a school or business in the US.
Grandparents, aunts, uncles, nephews and nieces are not considered "bona fide" relations under the latest rules.
Customs and Border Protection spokesman Dan Hetlage said his agency expected "business as usual at our ports of entry," with all valid visa holders still being able to travel.
But immigration and refugee campaigners said they would challenge the new requirements.
According to the regulations, those who cannot prove the close family connection will not be allowed into the US for the next 90 days.
A 120-day ban on refugees entering the country who cannot show the link has also taken effect.
The US Supreme Court only raised an injunction levelled against President Trump's travel ban proposal earlier this week.
The ban had been subject to a court block for a number of months.
Nevertheless, despite the lifting of the injunction, human rights groups have warned of fresh legal battles.
The American Civil Liberties Union, one of the groups challenging the ban, called the new criteria "extremely restrictive," ''arbitrary" in their exclusions and designed to "disparage and condemn Muslims."
Meanwhile, the National Immigration Law Center said the rules "would slam the door shut on so many who have waited for months or years to be reunited with their families".
President Trump, who made a tough approach to immigration a cornerstone of his election campaign, issued his travel ban via executive order shortly after taking office in January.
He argued the temporary measures were necessary to prevent terrorism until vetting procedures could be reviewed.