The American Civil Liberties Union says it has raised more than US$10 million (13.7 million) since yesterday.
It has also added more than 150,000 new members, the group's executive director told Yahoo News.
"What we've seen is an unprecedented public reaction to the challenges of the Trump administration," Anthony Romero, executive director of ACLU, told the news site.
The ACLU and other activist groups filed a class action lawsuit to challenge US President Donald Trump's executive order that banned travel to the US for citizens of seven Muslim majority countries: Syria, Iran, Libya, Somalia, Sudan, Yemen and Iraq.
Trump says it is a security measure.
A federal judge in New York issued an order temporarily blocking the Government from deporting people with valid visas who arrived after Trump's travel ban took effect.
Other judges have since also blocked parts of it.
But confusion remained about who could stay and who will be kept out. Federal courts in Virginia, Massachusetts and Washington state took similar action.
A more decisive ruling on the legality of the Trump action by US District Judge Ann Donnelly will probably take at least several weeks.
Trump's executive order is likely to face a series of new legal challenges about whether it violates a 1965 anti-discrimination law and the Constitution, scholars said today.
Trump's order cites seven Muslim-dominant countries, and the President has signalled he favours Christian entrants over Muslims. Four federal judges have put various holds on the law, and other courts are expected to consider similar stays. A group of 16 state attorneys general said they believe the executive order is unconstitutional, likely presaging an intense round of legal action against it.
Ruthann Robson, professor of law at City University of New York School of Law, said the fact that all four judges who had reviewed the order put various holds on it indicates that the measure faces serious challenge.
"When the federal judges are ruling on the injunctions, one of the requirements is that they have to say that there is a substantial likelihood that the plaintiffs will prevail on the merits," Robson said.
Robson is among the legal scholars who said the order could be thrown out on grounds that it violates the equal protection clause of the Constitution. She noted that courts have criticised governmental distinctions based on ancestry and race.
The wording of Trump's order in particular may expose it to legal challenges, experts said. It cites the need to protect the nation against a terrorist act such as those occurring on September 11, 2001 - even though the terrorists involved in that attack did not come from the seven nations cited in Trump's order, a fact that legal advocates are likely to cite in their challenges.
President Trump's executive order was not properly vetted
The order has caused much confusion since it was released. A spokesman for the Department of Homeland Security was quoted by the Reuters news agency as saying it applied to holders of green cards, who are legal residents. Yet White House Chief of Staff Reince Priebus said today on NBC that "it doesn't affect them". Later in the same broadcast, however, Priebus said, ''Well, of course it does [affect them]. If you're travelling back and forth, you're going to be subjected to further screening."
Such parsing of the order's meaning could be cited in legal challenges as evidence that it is unclear.
There were initial reports that the White House did not vet the order with the Justice Department, which led to widespread criticism on legal blogs and elsewhere that the measure was poorly conceived and thus open to legal challenge.
Senator John McCain and Senator Lindsey Graham said in a joint statement: "President Trump's executive order was not properly vetted. We are particularly concerned by reports that this order went into effect with little to no consultation with the Departments of State, Defense, Justice, and Homeland Security."
Priebus said officials throughout the government "knew full well what was going on".
Still, David Bier, an immigration policy analyst at the libertarian Cato Institute, said a key portion of the order, pertaining to legal residents, is illegal. He cited a 1965 immigration law stating that no person applying to be a permanent resident can be discriminated against based on gender, race or national origin.
Herald Online, AP, Washington Post