Senators unveiled a resolution on Thursday to block President TrumpDonald John TrumpNASA exec leading moon mission quits weeks after appointment The Hill's Morning Report — After contentious week, Trump heads for Japan Frustration boils over with Senate's 'legislative graveyard' MORE's emergency declaration to construct the U.S.-Mexico border wall.

Sens. Tom UdallThomas (Tom) Stewart UdallOvernight Defense: Details on Senate's 0B defense bill | Bill rejects Trump plan to skirt budget caps | Backfills money for border wall | Defense chief says more troops could head to Mideast Dem senator plans amendment to restrict military action against Iran Overnight Defense: Iran worries dominate foreign policy talk | Pentagon reportedly to send WH plans for 10K troops in Mideast | Democrats warn Trump may push through Saudi arms sale | Lawmakers blast new Pentagon policy on sharing info MORE (D-N.M.) and Susan CollinsSusan Margaret CollinsThe Hill's Morning Report - Trump says no legislation until Dems end probes Collins offering bill to boost battery research as GOP pushes energy 'innovation' Biden says Congress must move to protect abortion rights MORE (R-Maine) introduced the resolution on the Senate floor, where it's expected to be taken up within a matter of weeks.

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The two senators, in back-to-back speeches, stressed that the Senate's vote wasn't about whether a senator supported the U.S.-Mexico border wall or Trump but about maintaining a separation of power between the executive and legislative branches on funding the government.

“I support, strongly support, protecting the institutional prerogatives of the United States Senate and the system of checks and balances that is central to the structure of our government,” Collins said. 

Udall added that the debate over the emergency declaration was about the “strength of the rule of law.”

"This is about protecting the very heart of our American system of government. ... Congress and only Congress holds the power of the purse,” he said.

The Senate resolution, which is also being co-sponsored by Sens. Lisa MurkowskiLisa Ann MurkowskiMurkowski celebrates birthday with electric scooter ride Overnight Energy: Park Service plans to pay full-time staff through entrance fees | Oil companies join blitz for carbon tax | Interior chief takes heat for saying he hasn't 'lost sleep' over climate change Democrats grill Trump Interior chief for saying he hasn't 'lost sleep' over climate change MORE (R-Alaska) and Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenOvernight Defense: Details on Senate's 0B defense bill | Bill rejects Trump plan to skirt budget caps | Backfills money for border wall | Defense chief says more troops could head to Mideast Senate defense bill would pull Turkey from F-35 partnership if it buys Russian missile system Trump, Europe increasingly at odds on Iran MORE (D-N.H.), comes two days after the House passed its measure to block Trump’s emergency declaration.

All Democrats are expected to back the resolution once it comes to the Senate floor. They’ll need four Republican senators to get it to Trump’s desk, where he’s said he will veto it.

So far, three Republican senators have said they will vote for the resolution: Collins, Murkowski and Thom TillisThomas (Thom) Roland TillisThe Hill's Morning Report — After contentious week, Trump heads for Japan Collins offering bill to boost battery research as GOP pushes energy 'innovation' Lawmakers call for investigation after census hired registered sex offender MORE (N.C.).

Several other Republicans have voiced concerns about Trump’s emergency declaration.