While the Obama administration has sent some signals to states that it won’t interfere with the implementation of medical marijuana laws, the Drug Enforcement Administration in recent weeks has visited doctors who hold administrative positions with companies seeking dispensary licenses in Massachusetts and told them to resign or risk losing their registration to prescribe controlled medications.

The DEA officials have gone so far as to show up at the homes of doctors involved with prospective medical marijuana dispensaries, and at least two, but possibly more, physicians have already resigned their positions with medical marijuana organizations as a result, according to multiple sources.

“They’re going directly to the doctors, not setting up appointments, and giving them an ultimatum,” said Valerio Romano, an attorney in Boston who represents several applicants for dispensary licenses in Massachusetts. Romano founded Massachusetts Marijuana Compliance, a part of the VGR Law Firm.

The full impact of the actions by the DEA on the fledgling medical marijuana industry in Massachusetts remains unclear, but those involved in the industry say they worry that it could not only delay the state Department of Public Health’s licensing process even further, but also spook those in the medical community, many of whom are already wary of their role in the implementation of the voter-approved law legalizing medical marijuana.

“The main problem that I see with all this is the rollout for the program is already five-plus months behind and if the applicants are amending their applications to remove directors or members of the executive management team, this will just force the DPH to relook at the plans the applicants have,” Romano said.

Officials at the Department of Public Health said they have met with the DEA on drug diversion prevention issues related to registered marijuana dispensaries, but have not received any formal notification from the federal agency on warnings being given to doctors.

“Registered Marijuana Dispensaries are not required to have medical personnel on their management teams, and any doctor leaving the leadership team of an RMD would not cause any delays in the program or have an impact on applications beyond the additional time required to conduct background checks on replacement personnel,” the DPH spokesman David Kibbe said in a statement. “When Registered Marijuana Dispensaries experience changes in leadership, they are required to notify DPH. Any new RMD personnel must go through a comprehensive background check as part of the Department’s standard process.”

Paul Covell, the chief executive officer of the William Noyes Webster Foundation, said Dr. Carl Fulwiler, a Worcester psychiatrist and addiction specialist who was listed on the group’s dispensary license application as its substance abuse specialist, resigned after he was visited by the DEA last week.

“They told him you have to give up one or the other,” Covell told the News Service.

A spokesman for the New England division of the DEA did not returned several calls placed by the News Service over the past two days.

Covell said he did not think Fulwiler’s resignation would have a detrimental impact on his group’s application for a license, but said it does send a mixed message from the federal government about how the Justice Department will treat medical marijuana patients, doctors and business owners.

The William Noyes Webster Foundation received one of the 20 provisional licenses from the DPH in January to open a medical marijuana dispensary in Dennis. The DPH is currently in its verification phase of reviewing final applications.

“If he had been someone in an executive management position that might have caused us some concern, but he is in an advisory capacity and playing a minor role for us. I can’t speak for the others,” Covell said. “If this was the state doing it, that would be a different story. But if you look at other states that have legalized it, I think the barn door is wide open and my best guess is this thing will gather momentum.”

The U.S. House voted last month to prevent the Justice Department from stopping the implementation of medical marijuana laws in Massachusetts and other states. Two members of the nine-member Massachusetts delegation voted against the measure, which was part of a $51.2 billion appropriations bill.

Reps. Joseph Kennedy and William Keating joined 172 Republicans and 15 fellow Democrats in voting against the amendment, which would prevent the department from using the funds to stop 32 states and the District of Columbia from implementing laws authorizing the use, distribution, possession or cultivation of medical marijuana.

Medical marijuana advocates called the vote a "major victory" and said they expect the U.S. Senate to tackle a similar amendment this summer.

The DEA’s decision to focus on the licenses of doctors to prescribed controlled substances is not necessarily a new front for the agency to discourage the spread of medical marijuana, which it opposes, but it’s the first time Romano said he has heard of the department targeting those serving on boards or in administrative roles at medical marijuana companies.

In the late 1990s, following the legalization of medical marijuana in California, the DEA threatened to revoke the licenses of doctors who recommended medical marijuana to patients. The directive also authorized the U.S. Inspector General for Health and Human Services to exclude physicians from participation in Medicare and Medicaid programs.

The federal judge in Northern California overruled the DEA and affirmed the right of doctors to recommend medical marijuana to patients, which was all that was required to purchase the drug. The Ninth Circuit Court of Appeals upheld that decision for the 10 states in its jurisdiction, but the Supreme Court declined to take the case, which would have set a national precedent.