Medicare said Thursday that it does not have the power to reverse automatic spending cuts that are causing cancer clinics to turn away thousands of patients.

“We are unaware of any authority that could exempt Part B drugs from the sequestration requirements,” Medicare spokesman Brian Cook said.

The sequester is a series of across-the-board budget reductions that Congress allowed to go into effect when it could not agree on a spending plan earlier this year. As an unexpected consequence of the sequester’s cut to Medicare, cancer clinics are finding that they cannot afford to continue administering some chemotherapy drugs.

Ted Okon, executive director of the advocacy group Community Oncology Alliance, said he has heard from dozens of legislators in both parties interested in reversing the cuts.

“Some members have called over to Medicare and some want to start a letter to ask the administration to stop the cuts,” Okon said. “There’s really an outpouring of support.”

Others, including Rep. Joe Courtney (D-Conn.), argue that Congress — not the White House — needs to fix the law. He became aware of the issue after a clinic in his district notified patients it would stop seeing Medicare patients should the sequester come into effect.

“My sense is this is really Congress’s job,” Courtney said. “This was fully predictable because Medicare was not exempt from the sequester. It’s on our plate.”

Legislators had tried to shield Medicare by limiting its cut to 2 percent of its overall budget. That is a fraction of the cuts made to other federal programs.

But oncologists argue that the cuts have a much deeper effect on chemotherapy treatments because of the way they are covered. Medicare pays doctors who administer chemotherapy for the average sales price of the drugs, plus 6 percent for storage and other overhead costs.

Because doctors cannot change the price of the drugs, they say that the entire 2 percent cut must come out of the 6 percent add-on. That causes them to lose money on certain treatments, the doctors say.

“I don’t think legislators truly understood that the drug side was going to get hit,” Okon said. “I’ve had people ask if this is some kind of April Fools’ joke.”

Susan Greenberg, an oncologist in New Jersey, has begun urging patients she has turned away to call their members of Congress on the issue.

“The congressmen are our employees; they work for us,” she said. “I’m asking my patients to get out there and start complaining that their employees aren’t doing their jobs.”