MGM is also requiring all new hires, both hour and salary, to show proof of vaccination before beginning with the company.
The new vaccine mandate goes into effect Oct. 15, according to a letter distributed from staff of CEO Bill Hornbuckle.
"I know that for some of you this may be an unwelcome development," Hornbuckle said. "However, as one of the largest and most trusted operators and employers in our industry, MGM Resorts is determined to do our part to curb the spread of the virus and help counter alarming trends in cases, hospitalizations and deaths."
In late July Hornbuckle sent a letter to workers pleading them to get vaccinated or else face the risk of more restrictive measures like social distancing and capacity restrictions. Those measures, Hornbuckle said, could lead to furloughs and layoffs.
Last month the Clark County Commission mandated indoor mask wearing for all casino workers and guests.
Nevada was averaging slightly more than 1,000 new Covid cases per day across a seven-day average as of Aug. 16. By comparison, the seven-day average was below 300 for much of May and June.
In Mississippi, at least two casinos are requiring employees to be vaccinated. Scarlet Pearl Casino in D’Iberville was the first property in the state to enforce a mandate last month, while Beau Rivage handed down its own policy this week.
Beau Rivage salaried employees who do not work from home have to be fully vaccinated by Oct. 15.