Portland has joined Seattle in a lawsuit challenging President Donald Trump's executive order that threatened to withhold federal funding from sanctuary cities that refuse to help federal immigration enforcement.

The northwest cities are seeking a declaration that they are abiding by federal law and asserting that the Trump administration's threat to withhold federal funds is unconstitutional. Those funds, the lawsuit says, would otherwise go to home care for the disabled elderly and to food for children in need.

Mayor Ted Wheeler had announced in April that Portland would join Seattle's original lawsuit. The two cities made that official this week when they filed an amended complaint in the Western District of Washington.

The new filing notes that Portland ranks 11th among U.S. cities for resettling international refugees. The city relies on federal funding to help operate its police bureau and to help house vulnerable residents, it says.

The suit alleges Trump's order violates the Tenth Amendment, which prohibits the federal government from directing local and state governments to do the federal government's work. It also asserts that the order violates the U.S. Constitution's Spending Clause, which bans the federal government from using the denial of funds to coerce state or local action.

The cities also argue that the order violates the federal government's separation of power by surpassing congressional oversight of federal funds.

"It's not merely that our cities' values are under attack, it's that these attacks are against the law," Wheeler said in a statement. "Together, we are standing up for our values and the Constitution."

Two months after Trump's executive order threatened to withhold federal funds from sanctuary cities, Attorney General Jeff Sessions said in a March press conference that the federal government would also take "all lawful steps to claw back any funds" already awarded to sanctuary cities."

Seattle filed suit two days later.

"We are pleased to have the city of Portland join in Seattle's suit to protect our shared values," Seattle City Attorney Pete Holmes said in a statement.

In addition to asking the court to declare the relevant portion of the executive order unconstitutional and therefore void, the cities are asking that the Trump administration be required to pay their legal fees.

City Attorney Tracy Reeve said her office expects to do the bulk of the work on the lawsuit without outside counsel since Seattle already has counsel and took on much of the work by filing the suit.

Still, she said that could change. The city previously considered turning to a pro bono attorney outside the city.

"We're still finalizing arrangements for counsel," Reeve said.

--Jessica Floum

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