United Airlines Holdings Inc. said workers must get vaccinated against the coronavirus, becoming the first major U.S. carrier to impose the mandate.

Employees must receive the vaccine and upload their injection record to a company database no later than Oct. 25, although that date could change, United said in a memo Friday. In mid-June, the Chicago-based airline began requiring new hires to provide proof of coronavirus vaccinations by their start date.

United joins a growing list of companies that have been prompted by the rapid spread of a highly contagious virus variant to require proof of vaccination from employees, including Facebook Inc. and Tyson Foods Inc. Microsoft Corp. is requiring workers to have had the shots before they can enter any of its U.S. facilities. Others like Amazon.com Inc. and Wells Fargo & Co. have delayed the full reopening of their corporate offices.