Vice President Mike Pence will lead a commission to investigate President Trump’s baseless allegations of widespread “voter fraud.”

Voting rights advocates fear it could be the opening salvo in a federal effort to narrow access to the ballot box.

Trump told Fox News’ Bill O’Reilly during an interview broadcast Sunday that he would “set up a commission, to be headed by Vice President Mike Pence” to investigate the claims of widespread voter fraud the president has pushed for months without evidence.

Trump told O’Reilly that his claims did not “have to do with the vote, although that’s the end result. It has to do with the registration.”

“Look, Bill, we can be babies, but you take a look at the registration, you have illegals, you have dead people, you have this,” Trump said. “It’s really a bad situation. It’s really bad.”

Trump reportedly told congressional leaders after the inauguration that massive voter fraud cost him the popular vote and that 3 to 5 million illegal votes had been cast—claims with no basis in reality. Trump lost the popular vote by almost 3 million votes.

He said he would push for an investigation into the unsubstantiated claims. An executive action officially commissioning the probe has been stalled but is still planned, two unnamed senior Trump administration officials told NBC News.

A Washington Post review of voter fraud allegations in the 2016 presidential election found four cases out of more than 135 million votes cast.

“I will be asking for a major investigation into VOTER FRAUD, including those registered to vote in two states,” Trump tweeted in January. He added that he would also seek to investigate “those who are illegal” and “those registered to vote who are dead.”

“Depending on results, we will strengthen up voting procedures!” Trump tweeted.

The bipartisan National Association of Secretaries of State, which represents 40 state election officials, said in a January 24 statement that it is “not aware of any evidence that supports the voter fraud claims made by President Trump.”

The studies that the president has repeatedly cited as proof of voter fraud do not support his claim, according to the New York Times.

Brennan Center for Justice President Michael Waldman, whose organization works to safeguard and expand voting rights, noted in a statement that there is “no evidence of massive voter fraud—none. The notion that millions of people voted illegally two months ago, and nobody noticed, is preposterous on its face.”

An investigation “could easily devolve into a witch hunt. Worse, it could be used to justify sweeping voting restrictions,” Waldman added. “There is no need for another investigation that is not independent, rigorous, and fact based.”

“The facts are clear; the research has been done. Election officials, leaders of the President’s own party, and other leading election experts confirm that there is no evidence of election tampering as President Trump alone claims,” Karen Hobert Flynn, president of Common Cause, said in a statement.

“Rather than make false claims that result in voter suppression–our elected leaders should work to ensure that the backbone of our democracy, every eligible American’s right to vote, is made free, fair, and accessible,” said Hobert Flynn, whose nonpartisan organization works on voting rights.

Kansas Secretary of State Kris Kobach (R), a proponent of voter restriction, told the Wichita Eagle in January that he had “advised him (Trump) on the issue of voter fraud in multiple forms.”

“I know that he is interested in investigating the issue on a national scale, but I also know that he would like to see the Justice Department launch specific investigations where there is real serious, specific evidence of voter fraud,” Kobach told the publication.

Trump continually promoted falsehoods about voter fraud while on the campaign trail, even as his claims were repeatedly debunked. Like the Republican Party, Trump has voiced support for voter identification laws, which disproportionately keep people of color and people with low incomes from accessing the ballot box.