A Republican proposal to overhaul the tax code could endanger everything from employment services to health care for people with disabilities, advocates say.

More than a dozen disability advocacy groups are working furiously to block the U.S. Senate from passing a bill that may bring up to $1.5 trillion in tax cuts, warning that slashing such a huge chunk of federal revenue would spell trouble for programs that Americans with disabilities rely on.

“It is a significant threat to people with disabilities and would likely have a lasting impact on funding for critical services on which people with disabilities rely, including Medicaid,” said Alison Barkoff, director of advocacy for the Center for Public Representation.

Barkoff’s group and others including the American Association of People with Disabilities, the National Disability Rights Network and the National Council on Independent Living are pushing their members to contact senators during a national call-in day on Wednesday.

The Senate could vote as soon as this week on the tax bill, a version of which was already approved by the U.S. House of Representatives earlier this month.

Under existing budget rules, legislation that adds to the national debt must be offset. Accordingly, advocates say the proposed tax bill could lead to automatic cuts to federal programs like vocational rehabilitation and housing assistance.

“The proposed tax cuts will create enormous pressure on the federal budget,” said Julia Bascom, executive director of the Autistic Self Advocacy Network, which is involved in the national call-in day. “Both the administration and congressional leadership have made clear that they plan to alleviate that pressure by slashing Medicaid, including (home and community-based) waiver services, and other basic programs that allow people with disabilities to live good lives in our community.”

In addition, advocates say they are worried that the House version of the legislation would eliminate a tax deduction for those with high medical expenses and it would do away with tax incentives aimed at encouraging businesses to hire people with disabilities or make their facilities accessible.

Meanwhile, the Senate bill would end the Affordable Care Act’s requirement that all Americans have health insurance, a move that advocates say would destabilize the market, increase premiums and threaten protections for people with pre-existing conditions.

“This fight is, in some ways, even more important than the fights to save the Affordable Care Act because these bills could lead to the collapse of the ACA and devastating cuts and changes to entitlement programs and discretionary programs that support people with disabilities,” said Kim Musheno, vice president of public policy for the Autism Society.