Ed Bastian, chief executive of Delta Air Lines, informed employees on Wednesday that health insurance premiums for employees who had not been vaccinated against COVID-19 would increase by $200 a month from November 1, citing high fees for employees hospitalized because of COVID-19 infection.

Delta said employees who had not been vaccinated against COVID-19 would also face other restrictions, including an indoor mask rule with immediate effect and weekly COVID-19 testing starting on Sept. 12.

Bastian said in an employee memo: "the average hospitalization cost of Delta Airlines employees infected with COVID-19 is US $50000, and the surcharge of US $200 is necessary to address the financial risks posed to the company by unvaccinated employees. In recent weeks since the emergence of the variant of B.1.617.2 COVID-19, all Delta employees hospitalized by COVID-19 have not completed their vaccinations. "

Delta also said that from September 30, "according to state and local laws, COVID-19 's salary protection will be provided only to people who have been fully vaccinated but have experienced a breakthrough infection."

Bastian said about 75 per cent of Delta's about 75000 employees had been vaccinated against COVID-19. "the prevalence of delta variants means we need to get more people vaccinated and as close to 100 per cent as possible," Mr Bastian said.

Delta Airlines began requiring new employees to be vaccinated against COVID-19 earlier this year.

The aviation industry has been one of the industries most affected by COVID-19 's epidemic, and airlines such as Southwest Airlines and American Airlines say the spread of delta variants has had an impact on the recent recovery of the industry.