CHICAGO (NEXSTAR) — An internal message sent to employees of United Airlines is reminding its flight crews “never” to use tape to restrain unruly travelers.

The letter, dated Aug. 13, comes after a number of highly publicized incidents in which commercial airline flight crews used duct tape to secure disruptive passengers to their seats.

“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,” reads a portion of the letter, attributed to John Slater, United’s senior vice president of inflight services.

The letter begins with a thank-you to the airline’s cabin crew for remaining professional in the face of increasing cabin disruptions since the beginning of the coronavirus pandemic, noting that “most” of the disturbances were mask-related.

After mentioning another airline’s handling of an aggressive passenger, a man who was restrained with duct tape late last month, Slater congratulated United’s employees for using de-escalation techniques that are “different from some of our competitors.”

The remainder of the letter is used to remind crew of United’s policies for reporting and de-escalating interactions with difficult customers, and share safety updates (specifically regarding unintentional deployment of emergency slides) and details of the airline’s hiring plans, among other company news.

Slaters’ comments come in response to reports in recent weeks that airline crews had wrapped unruly passengers in duct tape until law enforcement cleared them to board. In July, American Airlines crew members taped a woman to her seat after she allegedly bit one of the flight attendants after trying to open a boarding door. The same month, Frontier crews used duct tape to restrain a 22-year-old man accused of groping a flight attendant, touching another inappropriately and punching a third.

Video shared to social media earlier this month showed a crew member duct-taping a disruptive teenager to his seat.

As reported by The Washington Post, United Airlines used tape to restrain passengers on separate occasions between 2003 and 2008. It was unclear if United’s previous policy allowed the use of tape during those incidents.

A representative for United was not immediately available to clarify which methods for restraint are allowed in the absence of tape. American Airlines, meanwhile, had previously confirmed a policy that allows for the use of both restraint tape and flex cuffs — essentially a type of plastic handcuff — which are included in flight attendants’ service kits.