California Rep. Steve Knight lost his cool and threatened to get physical with an angry anti-immigration protester who was rallying outside of his Simi Valley office last week.

In video of the incident, the Republican congressman is heard telling a protester "I'll drop your a**," during a heated confrontation over a bill that he signed.

The exchanged occurred when a protester shook Knight's hand, got into his face and accused him of voting for an amnesty bill. The protester then gave Knight a forceful pat on the shoulder. That's when Knight threatened him, saying "If you touch me again, I'll drop your a--, all right?"

The freshman rep went on denying that he ever supported amnesty and explained to the crowd why he voted in favor of the Homeland Security bill.

Knight voted for H.R. 240 earlier this year after conservatives added a provision that would have undermined President Obama's executive orders to protect millions of undocumented immigrants from deportation.

However, Knight told the protesters that the bill needed to be amended in order to pass in the Senate, or the Department of Homeland Security would have shut down. He added that Senate Democrats refused to pass the bill because it included a measure blocking Obama's executive action. As a result, the Senate remove the language regarding the immigration measure and sent a "clean" version of the funding bill back to the House.

"So the Senate stripped out the amnesty," said Knight in the video.

Although many conservatives rejected the Senate version of the bill, Knight was one of 75 Republicans to support it.

Still, Knight continued to argue with the protesters, saying that he is opposed to "amnesty."

"I have dealt with this group on several occasions and every time they try to escalate our conversations to a level that is not constructive," he said in a statement on Tuesday. "Over this past weekend, I lost my cool and I regret responding the way I did."

Watch the video below.