(Bloomberg) -- Sweetgreen Inc. is struggling to get workers to prove they’re vaccinated.

The restaurant chain, which filed for an initial public offering on Monday, said in its S-1 filing that it has had “significant challenges” getting employees to submit proof of Covid-19 vaccination. The company’s locations are concentrated largely in New York City, Los Angeles, Boston and the D.C. area, all of which have some level of vaccine mandate related to indoor dining.

Sweetgreen operates 140 restaurants in 13 states, with 33% of revenue coming from the New York City metropolitan area, according to its filing. To comply with New York regulations, the company is requiring New York City employees to show proof of at least one dose of Covid-19 vaccine by Dec. 1 or face termination. Diners in the city also must be vaccinated.

The company has recently resumed indoor dining at most of its locations. If President Joe Biden’s employer vaccination mandate goes into effect or Sweetgreen continues to operate in markets with indoor vaccination mandates, the chain could potentially face “significant employee layoffs, staffing shortages and related restaurant closures,” the filing warns.

The situation could exacerbate labor shortages already sweeping the restaurant industry. Sweetgreen noted in filing that the pandemic has put pressure on restaurants to improve wages, benefits and working conditions to attract and retain talent.

Indeed, the company has had higher turnover than others. In the year ended Sept. 26, about 172% of non-leadership restaurant employees left the company. Turnover in those jobs “increased significantly” in the third quarter of this year, the filing says. The industry average in 2020 was 130.7%, according to the Bureau of Labor Statistics. 

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