Delta Airlines is asking other airlines to also ban people on its no-fly list as part of its efforts to protect its employees and passengers. Since the U.S. had mandated mask-wearing on flights, the airline has collected listed more than 1,600 people who are now banned from flying on its airplanes.

Sources said the number of people on the no-fly list of major airlines in the country, which is separate from the federal no-fly list, had exceeded 4,000 people as of May. The number may have significantly increased over the past few months.

The growing figure doesn't take into account banned passengers by Southwest and American Airlines as the two companies have refused to share their no-fly list with the public or with other airlines.

Delta is reportedly now asking other airlines to share their respective no-fly lists to protect passengers and all employees across the industry. The airline reasoned that not sharing their lists of banned customers wouldn't really work as any banned passenger on one airline could just simply go to another airline.

Delta said it had also recently shared a list of 600 people, who had committed more serious offenses, to the Federal Aviation Administration. Most of those on the airline's banned list are unruly passengers and those that had refused to comply with the federal mask requirement.

Earlier in the week, the FAA said it had received 4,385 reports from airlines of unruly passengers since the start of the year. This included 3,199 incidents of passengers refusing to wear masks on flights. The U.S. Transportation Security Administration said the mask requirement for flights is still in force and will be effective until January next year.

Airlines began to enforce the federal mask mandate in June of last year. Due to an increase in incidents involving violators of the mandate, the FAA was forced to implement a zero-tolerance policy in January. So far, the agency has launched 789 cases against passengers since the start of the year.

The FAA and representatives of major airlines recently met to discuss new strategies to avoid confrontations and incidents aboard flights. The FAA had asked airlines to commit to doing more to reduce unruly behavior. For its part, the FAA said it is working with airports and law enforcement agencies to increase criminal prosecutions of passengers unwilling to obey the mandate.