If Donald Trump gets elected president, Muslims in the United States can expect a lot more surveillance in their mosques and communities. The Republican presidential candidate called in to “Morning Joe,” MSNBC’s morning news program, Monday to discuss how he would tackle the problem of Islamic extremism.

“You’re going to have to watch and study the mosques, because a lot of talk is going on in the mosques,” said Trump, adding that a New York Police Department surveillance program in which plainclothes police officers eavesdropped in Muslim neighborhoods had been scrapped by Mayor Bill de Blasio.

“From what I heard, in the old days, meaning a while ago, we had great surveillance going on in and around mosques in New York City. And I understand our mayor totally cut that out,” Trump said.

The NYPD’s program was shuttered in April 2014 under returning Police Commissioner William J. Bratton. The program had been a subject of two federal lawsuits and had received criticism from civil rights groups. While running for mayor, de Blasio said he was “deeply troubled” by the tactics, though he defended the program in the Wall Street Journal in 2012. His administration also fought the lawsuits that challenged the surveillance tactics.

Later in the segment, “Morning Joe” host Joe Scarborough said French officials were discussing shutting down mosques. “Is that something you would consider doing as president?” he asked Trump.

“Well, I would hate to do it, but it’s something that you’re going to have to strongly consider, because some of the ideas and some of the hatred, the absolute hatred, is coming from these areas,” Trump said.