Unruly passengers may have been duct taped to their seats on other carriers, but United Airlines officials want to make clear that they do not endorse the practice.
"Please remember that there are designated items onboard that may be used in difficult situations, and alternative measures such as tape should never be used," John Slater, senior vice president of inflight services, told employees in a Friday memo.
He encouraged crew members to follow de-escalation practices and to discuss "the situation with the Captain, Customer Service Representative and Ground Security Coordinator for evaluations and solutions," according to the memo.
A United spokesperson told NBC News that the policies were not new.
The memo comes amid a spike in dangerous behavior involving unruly passengers, including recent incidents where passengers were restrained using duct tape.
Earlier this month, passengers on a Frontier Airlines flight from Philadelphia to Miami duct taped a man to his seat after he groped two flight attendants and got into a physical fight with another, authorities said.
And in July, a woman aboard an American Airlines flight from Dallas-Fort Worth to Charlotte was duct taped to her seat by flight attendants after she tried to open the plane door midflight.
In a typical year, the Federal Aviation Administration said the agency sees 100 to 150 formal cases of bad passenger behavior. But from the start of this year to May, that number has jumped to 2,500, including about 1,900 passengers who refused to comply with the federal mask mandate, according to the FAA.