As the debate over the hotly contested American Health Care Act (AHCA) rages on, a group of 415 organizations and the Coalition to Stop Opioid Overdose sent a letter urging lawmakers in Congress to consider the ramifications that the AHCA will have on Americans living with addiction and mental illness.

The organizations—which include the American Academy of Pediatrics, the American Public Health Association and the National Alliance on Mental Illness—wrote the letter on behalf of the “millions of Americans suffering from addiction and mental illness who may lose their health care coverage” as a result of the AHCA.

“This coverage is a critical lifeline for these individuals, many of whom were unable to access effective treatment before the [Affordable Care Act’s] expansion of Medicaid eligibility to low-income adults,” reads the letter.

“The AHCA’s proposed changes to our health care system will result in reductions in health care coverage, particularly for vulnerable populations including those suffering from addiction and mental illness.”

The AHCA, proposed by the new Trump administration to replace Obama’s Affordable Care Act (ACA), is up for a vote in the House of Representatives on Thursday, March 23. Then it will have to win a majority vote in the Senate as well.

The bill proposes scaling back the ACA’s expansion of Medicaid, which would make it a much smaller program, notes Maggie Fox of NBC News. 

During a time of rising drug abuse and mental illness, the letter says it would be a mistake to reduce coverage for addiction and mental health—which were among 10 “essential health benefits” that all insurance plans were required to cover under the ACA.

“Rolling back the Medicaid expansion … will certainly reduce access to evidence-based treatments and reverse much or all progress made on the opioid crisis last year,” the letter reads. The ACA’s Medicaid expansion has “surely reduced the burden of the opioid misuse and overdose and suicide epidemics, and saved lives.”

Despite low approval ratings for Trump’s health care bill, the president remains confident that it will win over the American people in the end. “I think we are going to get a winner vote,” he said this week. “They want a tremendous health care plan. That’s what we have. There’s going to be adjustments to it, but I think we’ll get the vote on Thursday.”