Immigrants are coming over the U.S.-Mexico border to vote in the American election, Republican presidential nominee Donald Trump said Friday.

“They’re letting people pour into the country so they can go and vote,” Trump said at a roundtable meeting at Trump Tower in New York with members of the National Border Patrol Council. “You hear a thing like that and it’s a disgrace.”

It was the latest example of Trump warning the election will be “rigged,” a charge he tends to launch more frequently when polls show him losing ground against Democratic opponent Hillary Clinton, who has led for most of the race. Under U.S. law, only American citizens may vote; undocumented immigrants may not.

The fresh warning about vote-rigging seemed to emerge from a misunderstanding between Trump and one of the Border Patrol agents he was meeting with. The agents’ union endorsed him in March. A request for a fuller explanation from the Trump campaign wasn’t immediately answered.

Art Del Cueto, national vice president of the council, brought up the issue of immigrant voting during the roundtable, saying that agents were too overloaded with citizenship applications to handle deportation requests for undocumented immigrants apprehended with criminal records.

“I spoke to several agents in my sector who are in charge of processing,” he said. “At this point they are saying immigration is so tied up with trying to get the people who are on the waiting list to hurry up and get them their immigration status corrected.”

“Why?” Trump asked.

“So they can go ahead and vote before the election,” Del Cueto answered.

In September, Jeffrey Carter of U.S. Citizenship and Immigration Services told the New York Times that the agency had “anticipated that there would be a spike in applications this year, but the increase has exceeded expectations.”

In the first quarter of 2016, more than 252,000 U.S. residents applied to become naturalized citizens, a 28 percent increase from the same period a year earlier, according to the U.S. Department of Homeland Security in August. Mexican diplomats have mobilized for the first time to help immigrants to the U.S. gain citizenship.

But Trump interpreted Del Cueto’s remarks differently. “Big statement, fellas,” Trump told reporters in the room. “You’re not going to write it. That’s huge. But they’re letting people pour into the country so they can go and vote.”

The disparaging remarks Trump made about Mexican immigrants when he announced his presidential bid in June 2015 have dogged his campaign ever since.

“When Mexico sends its people, they’re not sending their best,” he said in his announcement speech. “They’re sending people that have lots of problems, and they’re bringing those problems with us. They’re bringing drugs. They’re bringing crime. They’re rapists. And some, I assume, are good people.”

At his first debate with Clinton on Sept. 26, Trump was asked whether he would accept the outcome of the election. “If she wins, I will absolutely support her,” Trump said. But he has since encouraged supporters to monitor polling places on Election Day.

Clinton’s campaign has noted the nonpartisan fact-checker PolitiFact’s report that Trump’s “rigged” election claim lacks evidence.

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