The Massachusetts state attorney general’s office says it’s reviewing complaints against testing sites statewide that were recently forced to shut down after operating without a license.

The state Department of Public Health on Thursday issued cease and desist letters to three testing sites in Worcester, Needham and Dartmouth — all run by the nationwide Center for COVID Control.

Each location said it provided free rapid antigen and PCR testing to people without appointments. But the sites never received licenses to operate a clinical laboratory and analyze the test results, health officials said.

Local and state authorities also received numerous complaints from residents about weeks-long delays receiving test results.

“They were sort of flying under the radar,” said Worcester Commissioner of Inspectional Services Christopher Spencer. “They were pretty new and you can see it just blew up all over the place.”

Spencer said the Center for COVID Control didn’t reach out to the state or localities about opening its Massachusetts sites. The Worcester site opened in a vacant storefront as a pop-up testing location, and it claimed to be at 1 Acton St. but was actually on Grafton St.

Worcester officials only became aware of the location and started investigating it once they received complaints about long lines outside and the delays receiving results, Spencer said.

A spokesperson for the state Attorney General’s office said it’s looking into whether the testing locations violated consumer protections or committed other wrongdoing.

The Center for COVID Control has received criticism about its testing sites around the country. Multiple states, including Oregon and Illinois, are also investigating the company, and the Better Business Bureau gave it an “F” rating.

In a statement, the Center for COVID Control said it’s "proud of its services,” but is temporarily halting operations as high consumer demand stresses staffing resources and affects “usual customer service standards.”

“Regrettably, due to our rapid growth and the unprecedented recent demand for testing, we haven't been able to meet all our commitments,” said Center for COVID Control founder and CEO Aleya Siyaj.

In Massachusetts, the company will have to receive proper licenses in order to reopen its locations.

Spencer said the testing locations requested insurance information from customers even though the tests were supposed to be free. He said he’s concerned the sites billed insurance companies without patients knowing.

“I don’t think they are sponsored by some wealthy benefactor to just do this for the public good,” Spencer said.

The attorney general’s office declined to say if it’s specifically looking into whether the Center for COVID Control inappropriately billed insurers. But asking for insurance information — even when a COVID test is free — is common at some testing sites.

As the current surge of the omicron variant continues, local and state officials say the closure of the three testing sites should not limit testing supply. Officials urge residents to find approved testing locations on the state Department of Health’s website.

“I would always encourage the public to go to reputable places — pharmacies that have licenses,” Spencer said. “And some of the other testing sites run by local hospitals and the Department of Health are always pretty good choices.”