WASHINGTON — Airlines have reported more than 500 cases involving unruly passengers since late December, and most started with passengers who refused to wear a face mask, federal officials said Wednesday.

The Federal Aviation Administration said it is reviewing more than 450 of the cases and has started enforcement action against about 20 people.

The FAA reported the figures shortly after it extended a “zero-tolerance” policy against unruly people on airline flights. The agency said under the policy, passengers who disrupt or threaten the safety of a flight could face fines and jail time.

The tougher enforcement stance was due to expire at the end of this month, but the FAA announced Monday it will stay in place as long as airline passengers are required to wear masks.