President Donald Trump’s temporary immigration ban faced on Monday the first of several crucial legal hurdles that could determine whether he can push through the most controversial and far reaching policy of his first two weeks in office.

The government has a deadline to justify the executive order temporarily barring entry of people from seven mostly Muslim countries and the entry of refugees after a federal judge in Seattle blocked it with a temporary restraining order on Friday.

The uncertainty caused by a judge’s stay of the ban has opened a window for travellers from the seven affected countries to enter the United States.

Trump has reacted with attacks on the federal judge and then the wider court system, which he blames for hampering his efforts to restrict immigration, a central promise of the Republican’s 2016 presidential campaign.

Democrats, meanwhile, sought to use Trump’s attacks on the judiciary to raise questions about the independence of his Supreme Court nominee, Neil Gorsuch.

The 9th US Circuit Court of Appeals in San Francisco over the weekend denied the Trump administration’s request for an immediate stay of the federal judge’s temporary restraining order that blocked nationwide the implementation of key parts of the travel ban.

But the court said it would consider the government’s request after receiving more information.

The government has until 3pm PST (2300 GMT) on Monday to submit additional legal briefs to the appeals court justifying Trump’s executive order. Following that the court is expected to act quickly, and a decision either way may ultimately result in the case reaching the US Supreme Court.

Top technology giants, including Apple, Google and Microsoft banded together with nearly 100 companies on Sunday to file a legal brief opposing Trump’s immigration ban, arguing that it ‘inflicts significant harm on American business.’

Noting that ‘immigrants or their children founded more than 200 of the companies on the Fortune 500 list,’ the brief said Trump’s order ‘represents a significant departure from the principles of fairness and predictability that have governed the immigration system of the United States for more than fifty years.’

The controversial executive order also ‘inflicts significant harm on American business, innovation, and growth as a result,’ the brief added.

Trump, who during his campaign called for a temporary ban on Muslims entering the United States, has repeatedly vowed to reinstate the Jan. 27 travel ban on citizens from Iran, Iraq, Libya, Somalia, Sudan, Syria and Yemen and a 120-day bar on all refugees in the name of protecting the United States from Islamist militants.

His critics have said the measures are discriminatory, unhelpful and legally dubious.

Ten former US national security and foreign policy officials, who served under both Republican and Democratic presidents, filed overnight a declaration in the court case against the executive order arguing the ban serves no national security purposes.

The declaration was signed by former secretaries of state including John Kerry, Madeleine Albright, Condoleeza Rice and former CIA Directors Michael Hayden and Michael Morell.

Bob Ferguson, the Washington State attorney general who filed the Seattle lawsuit, said he was confident of victory.

‘We have a checks and balance system in our country, and the president does not have totally unfettered discretion to make executive orders as he chooses,’ he told NBC News’ ‘Today’ show. ‘In the courtroom, it’s not the loudest voice that prevails... it’s the Constitution.’

On Sunday, Trump broadened his Twitter attacks on US District Judge James Robart in Seattle, who issued the temporary stay on Friday, to include the ‘court system.’ Trump a day earlier derided Robart, who was appointed by former Republican President George W. Bush, as a ‘so-called judge.’

‘Just cannot believe a judge would put our country in such peril,’ Trump tweeted on Sunday. ‘If something happens blame him and court system.’

Trump did not elaborate on what threats the country potentially faced.

It is unusual for a sitting president to attack a member of the judiciary. Vice President Mike Pence defended Trump, even as other Republicans urged the businessman-turned-politician to avoid firing such fusillades against the co-equal judicial branch of government, which the US Constitution designates as a check on the power of the presidency and Congress.

Democrats, still smarting from Republicans’ refusal last year to allow the Senate to consider former Democratic President Barack Obama’s nomination of appeals court Judge Merrick Garland to the Supreme Court, have seized on Trump’s attacks to question his nomination last week of Gorsuch.

‘With each action testing the Constitution, and each personal attack on a judge, President Trump raises the bar even higher for Judge Gorsuch’s nomination to serve on the Supreme Court,’ Chuck Schumer, the top Democrat in the Senate, said in a statement. ‘His ability to be an independent check will be front and center throughout the confirmation process.’

Republicans hope to swiftly confirm Gorsuch, a 49-year-old conservative appeals court judge tapped by Trump to fill the seat left vacant by the death of Justice Antonin Scalia nearly a year ago.