— -- The legal showdown over President Trump's executive action barring entry into the U.S. by people from seven predominantly Muslim countries is expected to produce another appeals court ruling as early as Monday and could ultimately go before the Supreme Court, experts told ABC News.
Where the Executive Order Currently Stands
After a federal judge issued a nationwide temporary restraining order blocking the executive action on Friday, airlines around the world were told it was back to business as usual regarding people's entry into the U.S. from the seven countries covered by the order -- Syria, Iraq, Iran, Libya, Yemen, Sudan and Somalia -- as well as refugees.
The 60,000 visas revoked under the executive action became valid again as long as the travel documents fulfilled the usual requirements.
Immigrant and refugee advocacy groups, concerned the executive order might soon go back into full effect, urged travelers to "book flights immediately."
An appeals court early Sunday ruled against a Justice Department request to immediately lift the judge’s order blocking the travel ban.
But the court still has to rule on the department's request to place an emergency stay on the judge's order to allow the government to resume enforcing the ban.
That decision could come as early as Monday, experts tell ABC News.
What Led to the Block on the Ban
Numerous lawsuits have challenged the president’s executive order, including some on behalf of travelers detained at U.S. airports and threatened with deportation in the hours after Trump signed the action on Jan. 27.
Among the legal challenges was one filed Jan. 30 by Washington and Minnesota, claiming they would suffer “irreparable harm” from the executive action's restrictions on travel.
U.S. District Judge James Robart in Seattle decided Friday in favor of the states' request for an immediate restraining order and placed a nationwide, temporary block on the travel ban.
"The executive order adversely affects the states' residents in areas of employment, education, business, family relations, and freedom to travel," Robart wrote, also citing damage to the missions of the states' universities and to the states' tax bases.
How the Trump Administration Responded to the Judge's Ruling
The Justice Department late Saturday night asked the Ninth Circuit Court of Appeals in San Francisco for both an immediate stay and an emergency stay to lift the restraining order, said Kate Shaw, an ABC News contributor and professor at Cardozo School of Law in New York City.
Lawyers for the department argued that the restraining order went "vastly overboard" and that it "second-guesses" the president who has authority over immigration and foreign affairs.
"The injunction contravenes the constitutional separation of powers; harms the public by thwarting enforcement of an Executive Order issued by the nation's elected representative responsible for immigration matters and foreign affairs; and second-guesses the President’s national security judgment about the quantum of risk posed by the admission of certain classes of aliens and the best means of minimizing that risk," the Justice Department lawyers wrote.
Their filing also cited a separate federal court opinion issued Friday in Massachusetts that rejected a request to suspend the executive order.
President Trump on Saturday referred in a tweet to this court ruling in Boston.
Where We Go From Here
Washington and Minnesota have until 1 a.m. PT Monday to file a response to the Justice Department's request to lift the block on the travel ban.
Then, the Trump administration will have until 3 p.m. PT Monday to respond to the states' filings.
Once all these filings are made, the Ninth Circuit judges will be able to make a ruling on whether to let the temporary restraining order stand or not.
What Happens If the Appeals Court Overturns the Judge's Ruling
If the court agrees to the Trump administration request, it may allow the federal government to again enforce the travel ban.
But that wouldn't necessarily mean the legal battle is over.
The ACLU told ABC News it expects to file a "broad challenge" in coming days to the executive action on immigration and refugees. And Shaw said the legal fight over the executive order titled, "Protecting the Nation from Foreign Terrorist Entry into the United States," could go to the Supreme Court.
"We anticipate filing a broad challenge to the executive order in the coming days on behalf of a variety of plaintiffs," ACLU senior attorney Lee Gelernt told ABC News.
"Right now there are a lot of cases because there was outrage over the executive order so people rushed into court to protect their clients, but it remains to be seen how the cases will fit together," Gelernt said.
ABC News' Jack Date, Michael Edison Hayden and David Caplan contributed to this report.