Restoring President Donald Trump’s ban on immigrants from seven mainly Muslim countries would “unleash chaos again”, lawyers for two US states argue.
Counsel for Washington and Minnesota urged a federal appeals court in San Francisco to maintain its nationwide temporary restraining order.
They are being backed by technology firms which say the travel ban is harmful to their businesses.
Trump administration lawyers are expected to respond later on Monday.
The restraining order was issued on Friday by a federal judge in Seattle, Washington, suspending Mr Trump’s executive order restricting immigration from seven mainly Muslim countries.
Visa holders from Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen will be allowed to enter the US until the full case has been heard.
The judge’s order received a furious response from Mr Trump, who claims national security is at risk.
The San Francisco appeals court has already turned down a Department of Justice request to set aside this temporary block, designed to allow the two states time to make their case that the ban is both unconstitutional and harmful to their residents, businesses and universities.
Their lawyers told the appeals court that any resumption of the ban “would reinstitute those harms, separating families, stranding our university students and faculty, and barring travel”.
They added: “Defendants now ask this court to unleash chaos again by staying the district court order. The court should decline.”
They also lodged a statement by a host of national security officials – including former secretaries of state John Kerry and Madeleine Albright, and former CIA director Leon Panetta – which describes the travel ban as ineffective, dangerous and counterproductive.