In response to the opioid epidemic that is killing tens of thousands of Americans a year, the U.S. government is poised to further restrict the amount of opioids Medicare patients can have access to at any one time, via a policythat would tell insurers to deny coverage for certain prescriptions on the spot. But a group of doctors and researchers is pleading with officials to reconsider, saying the move would harm cancer patients and others who desperately need pain relief.

In a proposal paper released last month, the Centers for Medicare and Medicaid Services (CMS) laid out two policies affecting opioid prescriptions obtained through Medicare Part D that would come into effect starting in 2019.

One would call for a “hard edit” of opioid prescriptions made to patients on Medicare Part D that exceed a specific cumulative daily dose—the equivalent of 90 milligrams of morphine (MME). When pharmacists go to fill these prescriptions by submitting the request electronically, they would encounter a denial of payment from the insurer or pharmacy benefit manager followed by a brief explanation of why. Patients could still be allowed to have their prescription paid by Medicare, but only after an appeal and acknowledgment from their doctor that they qualify for certain exceptions, such as having cancer, being terminally ill, or otherwise having pre-existing approval for a higher dose.

The second proposed policy would tell Part D plan providers to deny coverage for prescriptions made to first-time opioid users, flagged via a database that tracks prescriptions obtained through Part-D, that provide more than a 7-day-long supply, regardless of their diagnosis.

The new limits would be a step up from the current ones encouraged by the agency, which implement a “soft edit” for Part D prescriptions at 90 MME, and a hard edit for those at 200 MME. Soft edits still dictate that these prescriptions can be denied for coverage by the insurer, but the pharmacist can then approve it at the register based on their own judgement of the patient and their medical history. The CMS estimates that the change could affect up to 1.6 million Medicare patients, based on data showing the percentage of patients without an approved exception who received more than 90 MME worth of opioids for at least a day in 2016.