As Canada considers mandating federally regulated employees, such as airline workers, to be vaccinated, United Airlines says that it will require staff in the US to be vaccinated against COVID-19 by late October, perhaps sooner. The carrier is joining a rising number of big corporations that are responding to a surge in virus cases.

Company leaders called it a matter of safety and cited “incredibly compelling” evidence of the effectiveness of the vaccines.

“We know some of you will disagree with this decision to require the vaccine for all United employees,” CEO Scott Kirby and President Brett Hart told employees Friday. But, they added, “the facts are crystal clear: everyone is safer when everyone is vaccinated.”

United, which has 67,000 employees in the United States, was the first major US airline to announce it will require vaccination for workers and was joined later Friday by Frontier Airlines, which said all of its direct employees would need to be fully vaccinated against COVID-19 by Oct. 1.

“As we continue to watch the rapid increase of new COVID-19 cases across the United States caused by the Delta variant, I am concerned for the well-being of our team members, their families and friends,” said Barry Biffle, president and CEO, Frontier Airlines. “Safety is of the utmost importance at Frontier and we need to take every step possible for us to keep our teams safe, protect the operation and protect our passengers. The time has come to do what we can to help put an end to COVID-19.”

Frontier employees that choose not to or are unable to get vaccinated will be asked to provide proof of a negative COVID-19 test on a regular basis.

United, meanwhile, has been requiring vaccination of new hires since mid-June. Unvaccinated workers are required to wear face masks at company offices.

The Chicago-based airline estimates that up to 90% of its pilots and close to 80% of its flight attendants are already vaccinated. They get incentives to do so.

A United executive said the airline has no plans to require that passengers be vaccinated, calling that a government decision. The CEOs of Delta Air Lines and American Airlines have similarly ruled out a mandate for passengers.

United said US employees will need to be fully vaccinated by Oct. 25 or five weeks after the Food and Drug Administration grants full approval to any one vaccine – whichever date comes first. So far, the FDA has only granted emergency-use approval of the Pfizer, Moderna and Johnson & Johnson vaccines. Full approval of the Pfizer vaccine is expected soon, according to published reports.

Each employee will have to send an image of their vaccine card to the company. Those who don’t will be terminated, with exemptions granted only for employees who document religious or health reasons for not getting the shots, officials said.

Employees who are already vaccinated or do so by Sept. 20 will get an extra day of pay, according to the memo from Kirby and Hart.

The Air Line Pilots Association said in a note to members that a “small number of pilots” don’t agree with this new policy, but the union believes it is legal. The Association of Flight Attendants encouraged members to get vaccinated and said United’s announcement is not surprising because Kirby has spoken in favour of a mandate for several months.

The requirement won’t cover employees at smaller airlines that operate United Express flights.

Like United, Delta has operated vaccination centre for employees and recently began requiring the shots for new hires. Delta CEO Ed Bastian says that 73% of the airline’s workforce is vaccinated. Executives at other airlines have similarly encouraged their workers to get vaccinated, even offering bonuses and paid time off to get the shots, but haven’t made them mandatory.

Since the highly contagious delta variant became the leading strain of COVID-19 in the US, most airlines have said it hasn’t affected ticket sales. However, Frontier Airlines executives on Wednesday blamed the variant for weaker bookings in the past week.

Before the United announcement, Disney and Walmart announced vaccine mandates for white-collar workers, and Microsoft, Google and Facebook said they will require proof of vaccination for employees and visitors to their US offices.