The National Coalition on Health Care—a group of unions, health funds, providers and other organizations—on Tuesday urged lawmakers to renew federal funding so community health centers aren’t forced to close.

Under the Affordable Care Act and later the Medicare Access and CHIP Reauthorization Act, more than 1,200 facilities nationwide receive $3.6 billion in annual funding, which is roughly 70% of the federal funding available to them. The centers mostly treat low-income patients.

But this is the last year that funds are appropriated for the fund unless Congress acts to extend it. Community health center workers are on Capitol Hill this week asking Congress to renew the federal funding or else many will have to close.

“We’ll be closing health centers,” said Brenda Johnson, CEO of La Clinica Health Care, which has six community health centers in Oregon, during a Hill briefing Tuesday. “There are thousands of people who won’t receive care.”

Approximately 2,500 health center staffers are coming into Washington, D.C., starting Wednesday to lobby federal lawmakers to renew those funds, according to the National Association of Community Health Centers.

The trade organization is asking Congress to enact a five-year extension of the funds. It’s an issue they hope will receive wide bipartisan support, as MACRA did when it was passed.

Health centers have seen a boom in new patients in recent years thanks to coverage gains under the ACA, primarily through Medicaid expansion. More than 11 million people have secured coverage under the program’s expansion since 2014. Over half of health center patients in expansion states had Medicaid, according to Kaiser Family Foundation research.

The number of patients seen at community health centers has increased by 42% since 2008, hitting 25 million people nationwide as of 2017.