Washington (CNN) Democrats on Capitol Hill were quick to denounce President Donald Trump's announcement on Friday that he is signing a national emergency declaration over a border wall -- and promised to fight back against the executive action.

House Speaker Nancy Pelosi and Senate Democratic Leader Chuck Schumer called the move an "unlawful declaration over a crisis that does not exist," in a joint statement and warned that "Congress cannot let the President shred the Constitution."

Other congressional Democrats are vowing action to counter the emergency declaration, which the President said he was issuing at a news conference on Friday morning, and a day after Congress approved a spending deal to avert a shutdown, but which did not include the President's requested $5.7 billion in border wall funding.

Freshman Democratic Rep. Alexandria Ocasio-Cortez of New York tweeted on Friday that she and Democratic Rep. Joaquin Castro of Texas "aren't going to let the President declare a fake national emergency without a fight," in response to a report from Bloomberg that the lawmakers have plans to unveil legislation that would halt the declaration.

Castro put out a statement on Thursday saying that if the President invokes a national emergency over the border, "I'm prepared to introduce a resolution to terminate the President's emergency declaration."

House Democratic leaders plan to make it a top priority after recess to try to approve a resolution to block Trump's emergency declaration, but they are still trying to sort out exactly how that plays out, multiple sources involved in the discussions told CNN.

They are studying their various legislative options and multiple committees are likely to be involved, but the House Judiciary Committee might take the lead. With the House on recess next week, they have some time to discuss their options by the time they return to session.

According to federal law, Congress can rescind a presidential emergency declaration by passing a joint resolution. If the President vetoed the resolution, Congress could override a veto with a two-thirds majority in the Senate and the House.

If the House were to pass such a resolution, the Senate would be required by law to vote on the measure within 18 days.

House Judiciary Chairman Jerry Nadler said in a statement on Thursday that he would "fully support the enactment of a joint resolution to terminate the President's emergency declaration, in accordance with the process described in the National Emergencies Act, and intend to pursue all other available legal options."

Pelosi and Schumer argued on Friday that the President's action is a constitutional violation, but did not specify exactly what course of action they plan to pursue.

"The President's actions clearly violate the Congress's exclusive power of the purse, which our Founders enshrined in the Constitution. The Congress will defend our constitutional authorities in the Congress, in the Courts, and in the public, using every remedy available," the top two congressional Democrats said in their statement.

It has long been expected that if the President issued a national emergency over the border, the declaration would face an onslaught of legal challenges.

In a nod to that, Democratic Rep. Tony Cárdenas reacted to the news on Friday with a brief statement, saying, "Mr. President, we will see you in Court."

2020 Democrats react

Several 2020 Senate Democrats argued that there is no crisis at the border the way the President has portrayed it and that the emergency declaration itself is dangerous.

Sen. Kirsten Gillibrand of New York called the situation a "manufactured crisis," saying on Twitter, "Let's be clear on this: The only emergency at our border is the humanitarian one Trump created himself, by demonizing and ripping apart families. This manufactured crisis is racist, wasteful, and an outrageous abuse of power from someone too reckless and hateful to hold it."

Sen. Amy Klobuchar of Minnesota similarly warned , "Not getting what you want to fulfill a campaign promise/chant is not a national emergency. Taking money from real needs and emergencies is what will create an actual emergency."

Sen. Kamala Harris of California tweeted , "We should do something about the actual emergencies that plague our nation — like climate change or health care access — not playing politics in order to build a wasteful border wall."

Independent Sen. Bernie Sanders of Vermont, who has not announced a 2020 bid but is viewed as a likely presidential contender, s aid on Twitter that "The American people, the Congress and the courts must show Trump what the Constitution and separation of powers is about. Trump cannot declare a 'national emergency' whenever he wants, and spend money on his pet project. Not gonna happen!"

Democratic Sen. Sherrod Brown of Ohio, who is also viewed as a likely 2020 contender, called Trump "the real national emergency."

"These are all real emergencies that Trump does nothing about. But now, like a child who again has failed to get his way, Trump is trying to ignore the Constitution to build his unnecessary wall. Donald Trump is the real national emergency," Brown tweeted

This story has been updated with additional developments Friday.