Washington has become the first state to sue Donald Trump over his 'un-American and unlawful' immigration ban.

The state's attorney general declared that he was suing the President over his temporary order which affects seven countries with majority-Muslim populations.

Trump's executive order also suspended the United States' entire refugee program and set off nationwide protests over the weekend, including one that drew 3,000 people to Seattle-Tacoma International Airport.

'If successful it would have the effect of invalidating the president's unlawful action nationwide,' Attorney General Bob Ferguson said at a news conference.

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Bob Ferguson, Washington state's attorney general, declared that he was suing the President over his temporary order which affects seven countries with majority-Muslim populations

Trump's executive order also suspended the United States' entire refugee program and set off nationwide protests over the weekend, including one that drew 3,000 people to Seattle-Tacoma International Airport

Ferguson was one of 16 state attorneys general who released a statement Sunday calling Trump's immigration action 'un-American and unlawful.'

Trump has repeatedly said Friday's order suspending immigration for citizens of the seven countries for 90 days is aimed at protecting the nation against extremists looking to attack Americans and U.S. interests.

The lawsuit against Trump, the U.S. Department of Homeland Security and high-ranking Trump administration officials was filed in federal court in Seattle.

The complaint seeks to have key provisions of the executive order declared unconstitutional, Ferguson said. The state is also asking for a temporary restraining order against enforcement of the order.

'We are a country based on the rule of law, and in a courtroom it is not the loudest voice that prevails, it's the Constitution,' Ferguson said. 'At the end of the day, either you're abiding by the Constitution or you are not. And in our view, the president is not adhering to the Constitution when it comes to this executive action.'

Sara Lopez, of Seattle, holds a sign as she attends a Seattle City Council meeting in Seattle. Council members passed a resolution Monday reaffirming that Seattle is a 'welcoming city' that treats residents equally regardless of their refugee or immigration status

Technology companies Amazon.com Inc and Expedia Inc, both of which are based in Washington state's Seattle area, will support the state's suit, Ferguson said.

Another Washington state company, Microsoft Corp, said it has been cooperating with the attorney general's office to provide information about the order's impact 'in order to be supportive.'

'To our employees in the U.S. and around the world who may be directly affected by this order, I want you to know that the full extent of Amazon's resources are behind you,' Amazon.com Chief Executive Jeff Bezos said in a note to employees.

The complaint claims that Trump's actions are separating Washington families, harming thousands of state residents, damaging the state economy, hurting Washington-based companies 'and undermining Washington's sovereign interest in remaining a welcoming place for immigrants and refugees,' Ferguson said.

Washington state Governor Jay Inslee said the 'inhumanity' of Trump's order is obvious.

'This is un-American, it is wrong, and it will not stand,' Inslee said. 'The clear intent of this executive order is to discriminate against one faith amongst all God's children.'

A man holds a sign during a protest held in response to President Donald Trump's travel ban, in Seattle, Washington

Asked if he fears retaliation from the Trump administration, Inslee said 'there's no predicting this president, but we will not yield, we will not be leveraged, we will not be threatened, we will not be intimidated.'

Inslee said he learned the hard way over the years 'you do not back down to bullies.'

Ferguson said he has been in contact with other attorneys general but at this point Washington state was acting on its own regarding the legal action.

The Port of Seattle said over the weekend that people who were detained at Seattle-Tacoma International Airport as a result of Trump's order have been released.