MGM Springfield is laying off more than half its staff as of Monday.
The casino reopened last month with limited operations following a four-month closure ordered by Massachusetts officials to limit the spread of COVID-19.
"I understand the impact this will have on these employees and their families. Nothing pains me more than delivering news like this," CEO and President Bill Hornbuckle wrote in a letter to employees. "Please know that your leadership team is working around the clock to find ways to grow our business and welcome back more of our colleagues."
Across MGM Resorts, 18,000 furloughed employees will be laid off.
The state permitted Massachusetts casinos to reopen in July, under strict capacity and social distancing regulations, as well as limits on which table games are allowed. In its first three weeks under those rules, MGM Springfield reported $10.7 million in gambling revenue.
Several restaurants and the hotel at the Springfield resort remain closed. A company spokeswoman said the hotel will reopen when it can be done safely and there is enough demand.
The layoffs are a stunning reminder of the continuing economic costs of COVID-19.
MGM opened in western Massachusetts two years ago, with local officials championing its investment in the region. But even before the pandemic, the casino's revenue and employment numbers fell well short of the company's promises.
In addition, the company said laid-off employees can apply through the end of November for an emergency grant to help pay for things like rent, mortgage and groceries. MGM said the fund has raised more than $14 million since March, with more than $12 million distributed so far.
Correction: An earlier version of this report misstated the date by which MGM employees must be rehired in order to retain their seniority. The correct date is Dec. 31, 2021.