United Airlines’ CEO wants to make Covid-19 vaccines mandatory for employees and is encouraging other companies to do the same.

It’s a stance that differs from other airlines and companies in other sectors like retail and auto manufacturing.

“The worst thing that I believe I will ever do in my career is the letters that I have written to the surviving family members of coworkers that we have lost to the coronavirus,” CEO Scott Kirby said at an employee town hall Thursday, a transcript of which was reviewed by CNBC. “And so, for me, because I have confidence in the safety of the vaccine – and I recognize it’s controversial – I think the right thing to do is for United Airlines, and for other companies, to require the vaccines and to make them mandatory.”

United had more than 60,000 active U.S. employees at the end of 2020 and has sent recall notices to some 17,000 other workers whose jobs were cut last year.

Kirby acknowledged logistical challenges to getting staff vaccinated.

Airline employees are considered essential workers and are likely to receive the vaccine before many people. But the rollout so far has been slow and chaotic with the nation running behind targets.

Airline executives have said widespread vaccinations will help revive air travel demand as carriers grapple with billions of dollars in losses.

“I don’t think United will get away with and can realistically be the only company that requires vaccines and makes them mandatory,” he said. “We need some others. We need some others to show leadership. Particularly in the healthcare industry.”

In the staff note, it said it’s working with government officials and health-care providers to set up vaccine distribution centers at some of its big hubs.

Some employees have been hesitant to take vaccines.

“It’s certainly a sensitive topic all the way around,” Michael Klemm, president of the International Association of Machinists and Aerospace Workers District 141, which represents fleet and passenger service workers at United, said in an email. “We’ve received some frustration from members who don’t want to take the vaccine as well as concern from members who don’t want to work with someone who doesn’t take it.”

Klemm said the union members can file a grievance for any disciplinary action that results from their refusal to be vaccinated. If they object to being inoculated because of a religious belief or disability they can file complaints with the federal Equal Employment Opportunity Commission.

The United flight attendants’ labor union, the Association of Flight Attendants, said its focus is on ensuring vaccine access for crew members.

“Right now, Flight Attendants are in different tiers for access in each state,” AFA spokeswoman Taylor Garland said in a statement. “We need a federal approach that prioritizes Flight Attendants as essential workers facilitating interstate commerce.”

Other airlines haven’t said they plan to mandate vaccines.

Southwest Airlines last week said it does not “currently” require employees to get Covid-19 vaccines but said it strongly encouraged staff to do so.

American Airlines has a similar approach, telling employees last week that “We do not plan to require our team members to receive the vaccine unless vaccinations are ultimately mandated for entry to certain destinations.”

Delta Air Lines, meanwhile, said it is “actively working with all of the states to understand how Delta employees will be prioritized in the initial distribution of vaccines.”

The Atlanta-based carrier has encouraged employees to get vaccinated. On Wednesday the company told flight attendants their pay would be protected if they had a reaction to a vaccine that prevented them from working and that they would get an additional six hours of pay after receiving the second dose of the vaccine, according to a staff note seen by CNBC.

United told employees in a staff note this week to get vaccinated as soon as possible and not to wait for guidance from the airline.

Some companies are trying to persuade workers to get the vaccine by offering additional pay. Yogurt and food company Chobani said it will give employees in its manufacturing plants and offices up to six hours of paid time to get the two vaccinations.

So far, some retailers like Aldi, Lidl, and Dollar General, have announced similar plans to offer extra pay. Aldi said it would also like to open on-site vaccination clinics at its warehouses and offices to make it easy for workers to get the shots and eliminate the obstacles of getting child care or finding transportation.