Delta Airlines wants other carriers to help when it comes to protecting their flights by sharing their individual lists of unruly passengers, a company executive said on Friday.

Kristen Manion Taylor, senior vice president of in-flight service, wrote to flight attendants on Wednesday to inform them that the carrier has asked other airlines to "share their 'no-fly' lists to further protect airline employees." She added that passenger safety would not be effective if unruly customers can move between carriers.

Delta says its no-fly list has 1,600 names. United Airlines, a Delta competitor, is said to maintain a separate list of about 1,000 customers, according to The Independent.

Unruly customers have always been a cause of concern for customers, crew members and authorities, particularly during the COVID-19 pandemic. Attempts to enforce the federal mask mandate, in particular, have sparked incidents of violence and harassment of flight crews that have, at times, resulted in delays or forced landings in some cases.

This week, Sara Nelson, the president of the Association of Flight Attendants union, testified that the Federal Aviation Administration (FAA) had logged 4,284 "unruly passenger reports" since January when the Biden administration issued an order requiring passengers to wear masks on all flights.

Three-quarters of these incidents were related to a refusal to wear masks onboard and 61% involved passengers hurling racist, sexist or homophobic slurs. Nelson warned that if more was not done to cut down on these incidents then "there may be more incidents in 2021 than in the entire history of aviation.”

FAA data show that the number of incidents of airline harassment has been cut by 50% since instituting a zero-tolerance policy that has resulted in more than $1 million in fines to unruly passengers. However, the agency has said that the current rate of six incidents per 10,000 flights is "too high" for its liking.

To cut down further on this negative behavior, the Transportation Security Agency (TSA) was ordered by President Joe Biden to double existing fines for flouting mask mandates. Fines for first-time offenders would be $500 to $1,000 and repeat offenders would be made to pay up to $3,000 under the new executive order.

"If you break the rules, be prepared to pay," Biden said on Sept. 9 when announcing the new measure.

Another option that is being considered is cutting down on the availability of alcohol on flights. Neither American Airlines nor Southwest Airlines are selling alcohol over concerns on how drinking fuels bad behavior.

Rep. Peter DeFazio, D-Ore., said on Sept. 10 that airport restaurants should also get involved more by stopping the sale of to-go cups of alcohol to passengers.