United Airlines is taking a zero-tolerance policy toward the unvaccinated, with plans to fire employees who refuse to get the jab.

Companies around the world are rolling out mandates, requiring their employees to get vaccinated in order to return to work. Many companies are especially emphasizing mandates for employees that travel, given their increased risk of exposure.

United Airlines told Reuters that some 593 of its employees are at risk of being fired over refusing to comply with the mandate. The company had set a deadline of September 27, and will start firing the non-compliant as early as Tuesday.

“This was an incredibly difficult decision but keeping our team safe has always been our first priority,” Chief Executive Scott Kirby and President Brett Hart said in a memo, according to Reuters.