Former Maryland Gov. Martin O’Malley weighed in on Donald Trump’s controversial proposed Muslim registry Sunday, after Trump’s pick for White House chief of staff was pressed about the administration’s plans on Meet the Press.

Incoming Chief of Staff Reince Priebus said on Meet the Press Sunday the administration was not planning to implement a Muslim registry, but that he was “not going to rule out anything.”

“We’re not going to have a registry based on a religion,” Priebus said, according to NBC. “But what I think what we’re trying to do is say that there are some people, certainly not all people … there are some people that are radicalized. And there are some people that have to be prevented from coming into this country.”

O’Malley took to Twitter Sunday morning to respond to Priebus’ comments.

“If you want to create a religious registry of Americans, you can start with this Catholic,” wrote O’Malley in a tweet tagging both Trump and Vice President-elect Mike Pence.

The Anti-Defamation League, an organization dedicated to combating anti-Semitism and other types of discrimination, tweeted Thursday that members would register in solidarity if a Muslim registry was implemented.

In November 2015, Trump said he would “absolutely” require American Muslims to register in a database, but the president-elect has since walked back on those comments.

A Trump transition team spokesman wrote in a statement last week that Trump “has never advocated for any registry or system that tracks individuals based on their religion, and to imply otherwise is completely false,” The New York Times reported.

O’Malley and other Maryland politicians, including Minority Whip Steny Hoyer and Sen.-elect Chris Van Hollen, have been vocally critical of Trump’s appointees for top positions within his administration over the past week.

The former governor urged Americans on Nov. 14 to oppose the appointment of Breitbart executive Steve Bannon as White House chief strategist.

.@realDonaldTrump starts next 4 yrs by appointing racist/anti-Semite/xenophobe to run country. All decent Americans must oppose #SteveBannon
— Martin O’Malley (@MartinOMalley) November 15, 2016

Read my statement on the nominations of Sen. Sessions & Rep. Pompeo to natl security positions in Trump Admin: https://t.co/rlDLCixDup pic.twitter.com/7sizKHfLRx — Steny Hoyer (@WhipHoyer) November 18, 2016

Van Hollen also appeared on Fox 5 on Nov. 15 and expressed his concerns about Trump’s pick of Steve Bannon for chief White House strategist.

“He now is calling upon people to come together — that’s what he’s saying through his words. But people are also watching his deeds,” Van Hollen said. “So when he appoints someone like Steve Bannon … that creates a lot of anxiety. That is very troubling to have this guy who had what was called the alt-right website, sort of a white nationalist website.”