Homeland Security Secretary John Kelly on Tuesday bluntly challenged members of Congress critical of the Trump administration’s aggressive approach to immigration enforcement to either change the laws or “shut up.”

In a wide-ranging speech, Kelly also promised a border crackdown on marijuana, which is illegal under federal law but legal under state law in eight states and the District of Columbia.

The blunt-talking, retired Marine general defended the work of Homeland Security employees from immigration agents to airport security officers, saying they are unjustifiably maligned by critics as they enforce laws intended to keep America safe. He described Homeland Security staff as “political pawns” in his speech at George Washington University.

“They have been asked to do more with less, and less, and less,” Kelly said. “They are often ridiculed and insulted by public officials, and frequently convicted in the court of public opinion on unfounded allegations testified to by street lawyers and spokespersons.”

Kelly said the public and public officials should err on the side of assuming that the agency’s employees are acting within the law. And for members of Congress who don’t like the laws, Kelly said they “should have the courage and skill to change the laws. Otherwise they should shut up and support the men and women on the front lines.”

Critics have argued that the agency is too heavy-handed in enforcement operations, including arresting immigrants in the U.S. illegally whose only offense is being in the country without permission.

More than 21,000 immigrants in the U.S. illegally have been arrested since President Donald Trump took office in January, compared to about 16,000 people during the same time last year. About a quarter of those arrests were immigrants who had no criminal history, according to Immigration and Customs Enforcement.

While the number of deportations has actually decreased slightly since Trump took office, the crackdown has left immigrant communities and advocates worried that just about any immigrant in the country illegally could be swept up. During the Obama administration, ICE agents were told to focus strictly on immigrants convicted of serious crimes or those who otherwise posed a threat to public safety.

Kelly said stepped-up enforcement has had a dramatic effect. He said dangerous criminals are being arrested or are hiding, fearing that ICE is looking for them.

A sharp drop in arrests at the Mexican border suggests that fewer people have been trying to cross illegally since Trump took office.

In March, the U.S. Border Patrol arrested about 12,100 people trying to cross the border illegally. It was the fewest number of arrests in a month in at least 17 years. Border Patrol Chief Ron Vitiello said in a speech in San Antonio, Texas, last week that it was likely the fewest arrests in about 45 years.

In his remarks about drugs Tuesday, Kelly said arrests on marijuana charges will be used to bolster the case for deportation against immigrants in the country illegally, he said.

Kelly appeared to backtrack somewhat from comments in an interview with NBC’s Meet the Press that aired Sunday. Kelly said in that interview that the solution to drug problems in the United States was not “not arresting a lot of users. The solution is a comprehensive drug demand reduction program in the United States that involves every man and woman of good will.”