United Airlines this month will start requiring new hires to show proof that they have been vaccinated against Covid-19, following a similar move by Delta Air Lines.

The new rule requires external candidates with job offers made after June 15 to confirm they have been fully vaccinated by their start date, the Chicago-based airline said.

The move comes as companies are grappling with whether to require staff to get vaccinated or find a way to incentivize them get inoculated. United, Delta and American have offered extra time off or pay to employees who are vaccinated. Big employers like Walmart have taken similar measures.

“As we welcome new employees to the company, it’s important we instill in them United’s strong commitment to safety,” the airline said in a note to staff.

The new employees “will be required to upload their COVID vaccine card in My Info no later than 7 days post hire date,” the airline said. The company added it will evaluate any religious or medical circumstances of candidates who can’t be vaccinated.

United CEO Scott Kirby said in January that he wanted to make Covid vaccines mandatory for employees but the airline hasn’t taken that step.

Airlines spent much of the last year shedding workers but carriers like United have announced they will resume hiring of pilots and other positions as travel demand picks back up.