A coalition of groups organizing protests in the event President Donald Trump fires special counsel Robert Mueller has gathered thousands of pledges by individuals who say they’ll be ready to assemble on short notice at more than a dozen “Nobody is Above the Law” rallies across Colorado.

Groups have been preparing to mobilize nationwide protests and assembling participants since late summer but the number of people signing up has mushroomed in recent weeks, organizers said. The number of prospective protesters signed up for a Denver rally at the state Capitol, for instance, more than doubled from around 1,000 just before Christmas to more than 2,500 this week, said Katie F., a leader of the Indivisible Front Range Resistance and one of that event’s organizers.

“Trump’s solution to problems with people working for him has always been ‘You’re fired!’ He can’t keep doing this,” said Elizabeth H., organizer of the Fort Collins rally, on the event’s sign-up page. “Firing Mueller is a red line Trump cannot be allowed to cross – this abuse of power would trigger a constitutional crisis and nothing short of a national emergency. As citizens we need to stand up to this together, in solidarity.”

By Saturday morning, RSVPs were being taken for protests in 15 locations in Colorado – Alamosa, Boulder, Colorado Springs, Cortez, Denver, Durango, Edwards, Fort Collins, Grand Junction, Gunnison, Lakewood, Longmont, Loveland, Pueblo, and Salida.

Those who sign up agree to keep it peaceful, keep it legal and “strive to de-escalate any potential confrontations with those who may disagree with our values.”

According to a release issued by March for Truth, one of the national groups organizing the protests – via the TrumpIsNotAbovetheLaw.org website, which is mirrored by other groups taking part – more than 100,000 people had signed up by Dec. 18 to protest at more than 500 rallies in every state.

The site says the protests are supposed to start within hours of news breaking that Mueller has been fired – at 5 p.m. local time if Mueller is fired before 2 p.m. local time, and at noon the following day if Mueller is fired after 2 p.m. local time.

The websites devoted to planning the rallies includes a custom Facebook profile picture to demonstrate sympathy with the protests, a guide prepared by the ACLU to protesters’ rights, a dozen suggested chants – “Firing the top cop won’t make the investigation stop” – and tips to de-escalate violence and a video about handling disruption at an event.

“Americans are united in standing up for the fundamental principle that no one – including the president of the United States-is above the law,” said Karen Hobert Flynn, president of Common Cause, in a statement. “If President Trump obstructs justice by firing special counsel Mueller, tens of thousands of Americans are prepared to show up and protest such an abuse of power. We will put country over party and make clear that the rule of law must prevail.”

The protests are part of a nationwide effort put together by organizations including MoveOn.org Civic Action, Indivisible, the Center for American Progress Action Fund, March for Truth, Public Citizen, Pantsuit Nation, Mi Familia Vota, Stand Up America, Common Cause, Friends of the Earth, Women’s March, Democracy 21 and the People for the American Way.

Warnings that Trump might fire Mueller, who was appointed in May to oversee a federal investigation into links between Trump’s campaign and the Russian government, intensified in mid-December when congressional Democrats said they’d heard rumors the president was considering firing Mueller before Christmas.

Trump denied he was planning to fire Mueller – and Christmas came and went, with plenty of heated rhetoric about the Russia investigation but without the rumored firing.

Trump, Republican allies and conservative media, however, have been ramping up criticism of Mueller, his team of prosecutors, the Justice Department and the FBI – leading critics to warn the president could still act to end the investigation, which has led to felony indictments of two former Trump campaign officials and guilty pleas by two former Trump advisors.

If Trump ousts Mueller or otherwise attempts to curtail his investigation, the liberal MoveOn.org wrote on its website, it would provoke a “constitutional crisis” and “demand an immediate and unequivocal response to show that we will not tolerate abuse of power from Donald Trump.

“Our response in the minutes and hours following a power grab will dictate what happens next, and whether Congress – the only body with the constitutional power and obligation to rein Trump in from his rampage – will do anything to stand up to him.”