Epic Games employees working on the company’s smash hit Fortnite have had to maintain brutal work schedules, with many pulling 70- to 100-hour weeks to keep up with the game’s success, according to a new report published today. Fortnite’s rapid content release schedule has come at a cost of employee’s physical and mental health, and some have been fired from Epic for refusing to work overtime hours that the company officially says are “voluntary.”

According to an in-depth report by Polygon, the breakout success of Fortnite’s Battle Royale mode turned it into a cultural force and an economic powerhouse, earning Epic Games millions of dollars per day. But Epic’s employees have said maintaining the game has meant brutal work schedules.

“I work an average of 70 hours a week,” one employee told Polygon, speaking on the condition of anonymity. Most of the report’s sources could only discuss working conditions at the company if their names were protected, since most are under strict non-disclosure agreements. “There’s probably at least 50 or even 100 other people at Epic working those hours. I know people who pull 100-hour weeks.”