Donald Trump

President Donald Trump salutes a Marines honor guard as he disembarks from Marine One upon arrival at the White House Monday from a trip to Florida. (AP Photo/Manuel Balce Ceneta)

(Manuel Balce Ceneta / AP)

Oregon has officially signed on to support Washington State's lawsuit challenging President Donald Trump's executive order curtailing refugee immigration, Attorney General Ellen Rosenblum announced Monday.

Oregon is one of 15 states plus the District of Columbia that signed the joint friend-of-the-court brief filed with the Ninth Circuit Court of Appeals.

In the brief, states outline the many ways they were harmed by the immigration ban and would be further harmed if it were reinstated, including losing college professors, college students, medical students, doctors, tourists and business travelers barred or deterred from entering the country.

Washington's attorney general challenged the executive order in court last week, which resulted in a federal judge applying a temporary hold on implementing the executive order. The U.S. Department of Justice has appealed that ruling.

If the Court of Appeals were to send the case back to a trial court, Oregon may offer legal resources, the state attorney general's office said.

"We want to be ready to help in any way we can to establish the permanent illegality of the Executive Order," Rosenblum said in a statement.

Separately, Oregon and Washington plan to jointly ask the Washington judge to allow an amendment to add Oregon to the lawsuit, Rosenblum's office said. She said that action could come as soon as Tuesday.

Oregon's involvement in the lawsuit comes days after Gov. Kate Brown asked Rosenblum to "explore legal remedies" for resisting Trump's actions in court.

Trump's order temporarily shuts down legal refugee immigration program and indefinitely halts refugee immigration from seven majority-Muslim nations.

-- Gordon R. Friedman

gfriedman@oregonian.com; 503-221-8209