President Donald Trump on Thursday signed an executive order that would deny colleges certain federal research and education grants if they failed to comply with free speech standards outlined by the administration.

"Under the guise of speech codes and safe spaces and trigger warnings, these universities have tried to restrict free thought, impose total conformity and shut down the voices of great young Americans ... all of that changes starting right now. We're dealing with billions and billions and billions of dollars," Trump said, surrounded by student activists at a White House ceremony Thursday afternoon.

In doing so, Trump is responding to a rallying cry among conservatives who say their views are suppressed on campuses, and that speakers are sometimes assaulted or silenced when protesters threaten violence.

Trump called the move "historic," saying that students and American values have "been under siege," as several students said free speech is at risk on their campuses.

"Every year the federal government provides educational institutions with more than $35 billion in research funding. All of that money is now at stake. That's a lot of money. They're going to have to not like your views a lot," Trump said.

The executive order would direct 12 grant-making agencies to work with the Office of Management and Budget to ensure universities are complying with federal law in an effort to promote free speech on college campuses, the senior administration official said earlier Thursday during a phone call with reporters.

Critics argue Trump's move is an attempt to fix a non-existent problem and one notable is Republican Sen. Lamar Alexander of Tennessee, chairman of the Senate Health, Education Labor and Pensions Committee.

In a statement on Thursday, Alexander said he didn't "want to see Congress or the President or the department of anything creating speech codes to define what you can say on campus."

"The U.S. Constitution guarantees free speech. Federal courts define and enforce it. The Department of Justice can weigh in. Conservatives don’t like it when judges try to write laws, and conservatives should not like it when legislators and agencies try to rewrite the Constitution," Alexander said.

At the same time, he said he agreed with the Trump administration's position that colleges "should provide better data on student debt and put some ‘skin in the game’ to reduce student borrowing."

Suzanne Nossel, the CEO of PEN America -- an organization that works to defend free expression rights, including free speech on college campuses -- said in a phone interview that the federal government "can have a role in reinforcing the principles of the First Amendment and the commitment to freedom expression and academic freedom at public universities in particular."

"But when you get into the possibility of punitive measures and the withholding of federal funds based on, you know, particularly kind of very vague definitions of, you know an idea like free inquiry. That's worrisome," Nossel added.

Following Trump's preview of his executive order in a fiery speech earlier this month at the Conservative Political Action Conference, 11 groups, including the American Association of University Professors and the American Federation of Teachers, issued a joint statement calling the proposal "a dangerous solution to a largely nonexistent problem."

"While the specific provisions of the promised executive order have not been revealed, like such legislation they are liable to interfere with institutional autonomy and governance in ways that is more likely to stifle than encourage free expression and diversity of opinion," the statement said. "There are and always will be individuals on campus and in society generally who wish to silence those with whom they disagree. But punitive and simplistic measures will only exacerbate the problems they may create," the statement said.

Though the administration official who briefed reporters stressed that free speech rules already apply to higher education institutions, the official said the order is designed to provide better oversight and enforcement by making free speech a more explicit condition of compliance.

Public universities will have to agree to follow the guidelines as a condition of receiving these grants, while private universities will have to certify following their intended policy, the official said.

The executive order would not affect student aid money, and would also require the Department of Education to publish information on earnings, debt, default rates and loan repayment rates to the college score card, the senior administration official said.

The official declined to say whether the president believes the issue has worsened in recent years, not wanting to get ahead of the president’s remarks. “The president is fully committed to promoting free speech on college campuses,” the official said.

The order would also require the Department of Education to submit policy recommendations to the president about institutions sharing the financial risk of student loans, the official said.

Trump had publicly teased the executive order during his CPAC speech and had also tweeted about the issue, in one instance writing: “If U.C. Berkeley does not allow free speech and practices violence on innocent people with a different point of view - NO FEDERAL FUNDS?”

"Just the fact that the President first announced this at CPAC, the fact Jeff Sessions when he was attorney general making a speech in front of Turning Point USA, a conservative group, this issue, you know, kind of adds this ideological cast," Nossel of PEN America said. "You know, really the First Amendment is nonpartisan. It doesn't have any ideological bias. It protects speech from across the spectrum. And so, the fear here is that you know, this is not just about protecting all kinds of speech it's about protecting certain kinds of speech and I think that's the way the executive order is implemented it's highly problematic."

But when it comes to the actual implementation of the order, the official was short on details and deferred the matter to OMB.

“I don't want to get ahead of implementation, that will be coming in the next several weeks, months,” the official said.