US President Donald Trump's order to block arrivals from six mainly Muslim countries takes partial effect yesterday after he won a Supreme Court victory over rights groups.

But implementation of the order after five months of legal challenges could be chaotic, in part due to the meaning of a key term used in the court's ruling Monday: "bona fide."

The court said that Trump could only ban travelers from the targeted countries "who lack any bona fide relationship with a person or entity in the United States."

With a 72-hour preparation period set before implementing the ban, the ruling has sent lawyers diving into legal texts to define that.

They need to set standards for US immigration officials and diplomats in Iran, Libya, Somalia, Sudan, Syria and Yemen, and also at US arrival points, who will decide who from those countries can still enter the United States.

Lawyers and advocates both for and against the travel ban say the result could be a flood of legal challenges by travelers, immigrants and their supporters -- further slowing arrivals from the six countries.

Immigrant advocates were preparing for the onset of the ban, saying they would be at airports to aid any arriving travelers that immigration officers seeks to send back.

The ruling Monday capped five months of heavily politicized legal scrapping. The highest US court partially reversed lower courts' freezes of Trump's 90 day ban on travelers from the six countries, which he said was necessary to screen out potential terror threats.

It also allowed Trump to implement a 120 day ban on all refugees.

The court said it will review the overall case in October, meaning both bans will largely have run their course by then, though they could be extended if immigrant vetting processes are still judged to be too weak.

Even with the ban being blocked for five months, arrivals from the six countries have plunged due to more rigorous vetting. Arrivals were down by about half in March and April, just 6,372, compared to 12,100 for the two months in 2016.