WASHINGTON (CN) — House Democrats introduced a resolution Friday to block President Donald Trump’s effort to fund his long-promised wall along the U.S-Mexico border by declaring national emergency.

Formally setting off a showdown between Congress and the White House, the resolution was submitted this morning by Representative Joaquin Castro, a Texas Democrat who chairs the House Hispanic Caucus.

The move comes one week after Trump announced he was declaring a national emergency to free up money for his wall.

Castro had been publicly discussing his intention to introduce the resolution for more than a week, starting when the White House first confirmed Trump’s plan to declare an emergency.

Under the National Emergencies Act, Congress can terminate a president’s national emergency declaration by passing a resolution through both the House and the Senate. Because the bill would need Trump’s signature, it will essentially require veto-proof majorities in each chamber in order to take effect.

In a dear-colleague letter sent out earlier this week, Speaker of the House Nancy Pelosi, D-Calif., encouraged members to cosponsor Castro’s resolution, saying the House will vote on the measure within the next 18 days.

“President Trump’s emergency declaration proclamation undermines the separation of powers and Congress’ power of the purse, a power exclusively reserved by the text of the Constitution to the first branch of government, the legislative branch, a branch co-equal to the executive,” Pelosi wrote in the letter.

Castro announced Thursday that the resolution had 222 cosponsors.

Apart from opposition in Congress, Trump’s declaration last week of a national emergency spurred a host of legal challenges in courts across the country..

More From Missoula Current