President Donald Trump promised Monday to prosecute anyone caught voting illegally in the mid-term elections.

“Anyone caught will be subject to the Maximum Criminal Penalties allowed by law,” Trump wrote on Twitter. “Thank you!”

Trump said that all law enforcement officers had been notified to monitor Tuesday’s elections for illegal voting.

The president has a long history of campaigning against election fraud and even launched a federal investigation on the issue in 2017.

The attempt stalled, however, after states refused to turn over their election data.

In January, the president urged the United States to shift to a system that required Voter I.D. to end a “rigged” system.