U.S. immigration officials are waiting for guidance on how to enforce President Donald Trump's revived travel ban, which could be implemented as early as Thursday morning.
Officials at the departments of State, Justice and Homeland Security were still unclear on exactly who is to be allowed in from six Muslim-majority nations and who is to be kept out.
Those six nations are Iran, Libya, Somalia, Sudan, Syria and Yemen.
The Supreme Court on Monday partly reinstated the travel ban, which was blocked by two lower courts on the ground that it is unconstitutional. The justices ruled that until they hold hearings on the ban, only visitors who can prove that they have a "bona fide relationship" in the United States will be admitted.
But the court did not spell out what constitutes a bona fide relationship, leaving government lawyers to spell it out and U.S. customs and immigration officers scratching their heads.
The Department of Homeland Security assured travelers Wednesday that they would not see any of the chaos that ensued when the travel ban was introduced in March. It promised it would implement the revised ban "professionally with clear and sufficient public notice."
Some U.S. immigration lawyers said many of their clients from the six affected countries were still filled with uncertainty. A number of attorneys planned to set themselves up at international airports, ready to offer help.
Trump signed an executive order in March temporarily barring travel to the U.S. and refugee resettlement from the six nations plus Iraq, which was later dropped when the order was revised.
The White House said the pause was to give authorities time to strengthen vetting procedures.
Trump has said he has the authority to impose a travel ban as part of his obligation to keep the American people safe. But federal courts in Hawaii and Maryland ruled the ban targeted Muslims and violated the U.S. Constitution's prohibition of religious discrimination.
The Supreme Court agreed to hear arguments for and against the travel ban and partially reinstated it until the case can be scheduled.