MONTPELIER, Vt. — Those involved in Vermont’s struggle to stem opiate abuse are watching warily as a major chain of drug testing centers faces an investigation that could bring the largest Medicaid fraud settlement in state history and possible closure of labs considered crucial in the opiate fight.

Meanwhile, as a group of investors presses for emergency approval from the state Green Mountain Care Board for a takeover of Burlington Labs, the attorney general’s office is urging the board not to grant any such approval until allegations of Medicaid overbilling are resolved.

Burlington Labs is seen as a key player in keeping recovering addicts accountable to their treatment programs. The head of a treatment program in Middlebury said if the Burlington Labs collection center there closed, addicts in rural Addison County likely would have to travel an hour or more to Burlington or Rutland to provide urine samples for drug testing.

“A lot of these folks don’t have a way to get to drug testing that is part of their medication-assisted treatment,” said Bill Prim, director of the Turning Point Center.

Patrick Lamb, a Chittenden County deputy state’s attorney who works at the specialized drug treatment court in Burlington, said drug testing is key to keeping those brought in for drug offenses accountable without resorting to incarceration.

About 90 percent of drug offenders ordered to undergo urinalysis use Burlington Labs, whose headquarters is near the courthouse, Lamb said. If Burlington Labs were to close, it would mean clinicians would be spending more time helping offenders find a way to take the test instead of focusing on strategies to help them beat their addictions, he said.

In letters sent to the Green Mountain Care Board, the state panel that regulates health care, Burlington Mayor Miro Weinberger and the heads of human services nonprofits urge that Burlington Labs be kept open.

Elizabeth Wohl, a lawyer for a group of investors looking to acquire and rescue the financially troubled Burlington Labs, wrote to the board Aug. 19 about the company’s troubles: It had defaulted on nearly $4.9 million in bank financing, owed other creditors nearly $3.7 million and had recently negotiated a $6.5 million settlement of allegations that it had overbilled the joint state and federal Medicaid program.

Burlington Labs issued a statement saying the overbilling was the result of unintentional coding errors. It denied any wrongdoing.

Jason Turner, head of the Medicaid fraud unit at the attorney general’s office, said no settlement had been reached. If the settlement did end up at $6.5 million, he said, that would be the largest Medicaid fraud settlement in state history.

Wohl urged quick approval of the proposed acquisition. She wrote of the “near certainty that Burlington Labs will cease doing business” if the takeover were not completed in 30 days.

But Turner wrote to the board Friday saying the attorney general’s office doesn’t want the takeover plan approved until the Medicaid fraud settlement has been finalized and the acquiring investors have agreed to its terms.

“Ensuring that the state of Vermont and the United States receive appropriate compensation” from the settlement “should be a critical consideration in determining whether the application should be granted,” he wrote.