BOSTON — A company that runs three cannabis dispensaries in Massachusetts failed to properly pay employees who worked Sunday and holiday shifts, according to the state attorney general’s office.

Theory Wellness, with locations in Great Barrington, Chicopee and Bridgewater, has been ordered to pay $300,000 in restitution and penalties after an eight-month investigation, according to a statement from the office. The company also has three locations in Maine in South Portland, Waterville and Bangor.

Under Massachusetts law, employees of certain retail businesses are entitled to “premium pay” for working Sundays and certain holidays. In 2021, that rate is 1.2 times their regular hourly rate. That rate will go down to 1.1 next year and will be eliminated in 2023.

The attorney general’s office started investigating in December after getting a complaint from an employee. The state determined that more than 280 Theory Wellness workers did not receive the proper premium pay.

Theory Wellness in a statement said it cooperated with the attorney general’s office over what it called “inadvertent payroll errors.”

“Most importantly, we had the opportunity to provide additional compensation to the former and current members of our team who were affected to resolve this matter swiftly,” the statement said.