By Jonathan Stempel

NEW YORK (Reuters) - JPMorgan Chase, the largest U.S. bank, has begun suing customers for check fraud, saying they improperly withdrew funds by taking illegal advantage of a temporary technical glitch that went viral on TikTok.

The glitch in late August let customers deposit big checks in ATMs and withdraw funds immediately before the checks could clear, even if the checks later bounced.

Chase filed four lawsuits on Monday in federal courts in Los Angeles, Houston and Miami, accusing two individuals and two businesses of illegally retaining more than $661,000 after the checks they deposited were deemed counterfeit or forged.

In the largest case, Chase said a Houston man still owes $290,939.47 after withdrawing over two days most of a $335,000 check that a masked man deposited in his account on Aug. 29. Chase said the check was rejected on Sept. 4.

The defendants did not answer, did not accept, or could not immediately be reached with messages seeking comment on Monday.

All four lawsuits accuse the defendants of violating their deposit agreements, and seek the return of improperly withdrawn funds plus other costs.

JPMorgan, based in New York, said it is pursuing the cases and cooperating with law enforcement to ensure that people are held accountable.

Last month, the Wall Street Journal said the bank was investigating thousands of possible check fraud incidents.

"Fraud is a crime that impacts everyone and undermines trust in the banking system," JPMorgan spokesman Drew Pusateri said in a statement.

Check fraud is a federal crime. Many banks including Chase let customers access some of the value of their checks until the checks clear.

(Reporting by Jonathan Stempel in New York; Editing by Richard Chang)