A law that provides medical monitoring and treatment for Sept. 11 first responders expired at midnight Wednesday due to the failure of Congress to act.

For now, first responders who rushed to the World Trade Center after the 2001 terrorist attacks, worked for weeks and now suffer from illnesses like pulmonary disease and cancers will still be able to get their health care. But federal officials who administer the program say it will face challenges by February and will have to start shutting down by next summer.

Letting the program expire creates "enormous anxieties and fears in the minds of very sick people," said Sen. Kirsten Gillibrand, D-N.Y., who has been lobbying her colleagues to make the program permanent and recently was joined by comedian Jon Stewart.

New York City Mayor Bill de Blasio said it was unacceptable for Congress to let it expire.

"Congress must stop putting politics ahead of our heroes' health," he said in a statement.

The Sept. 11 program is one of several that will expire at midnight due to congressional inaction. While Congress moved toward passing legislation to keep government agencies open, there are some programs that depend on further action to operate long-term.

John Feal, a former World Trade Center demolition worker and leading advocate for sick responders, has pressed lawmakers to pay attention to the Sept. 11 program.

"People are dying and suffering, and Congress can easily close this wound," Feal said. "But they continue to add salt to it."

The Zadroga Act, named after a responder who died after working at ground zero, first became law in 2010 after a debate over the bill's cost. Proponents are seeking the law's permanent extension in part because some illnesses may not manifest until years later, after the statute of limitations for worker's compensation or certain state laws may have run out.

House Republicans have been supportive of the program but have opposed its permanent extension because they say they want the chance to periodically review it and make sure it is operating soundly. The Senate has not moved a bill.

In a letter to the Senate, Centers for Disease Control and Prevention Director Tom Frieden said if the law isn't extended, the World Trade Center Health Program "will begin to face significant operational challenges" by February. By next summer, the program's 72,000 enrolled beneficiaries will have to be notified that they may not receive health care beyond September 2016 and the program will have to start to shut down. Frieden said that process could cause patients additional stress.

Earlier this summer, Dr. John Howard, the administrator of the CDC program, told a House panel that extending the law would help clinicians treat victims and allow administrators to better plan patient care.

"It's stressful to be told on a year-to-year basis that your care might be taken away," Howard said. "From the administrative perspective, it's stressful because we have to constantly prepare for when this may end."

Other laws set to expire at midnight tonight:

—Federal Perkins Loan Program. The House passed a bill Monday to extend the student loan program, which provides low-interest loans as one alternative to more expensive private student loans. But Sen. Lamar Alexander, R-Tenn., on Wednesday blocked an attempt to extend the law in the Senate.

Alexander said the rate for Perkins loans is higher than other loans and he wants Congress to replace the program with simpler loans that have lower interest rates and more generous repayment plans. He said students who have Perkins loans now will not be affected.

Education Secretary Arne Duncan has called on Congress to expand and better target the program. "Perkins is an important campus-based financing tool to help lower and middle income students cover any remaining need after other aid has been applied," he said.

—Land and Water Conservation Fund. The Interior Department program invests earnings from offshore oil and gas leasing to protect federal public lands and waters. Expiration will mean that the government isn't authorized to collect some of the offshore royalties, decreasing revenues for local conservation, restoration and historic preservation projects across the country.

—Child nutrition. Renewal of the 2010 law that oversees school meal programs, summer feeding programs, the Women, Infants and Children program and other government institutional food aid has been stalled as lawmakers debate its cost and whether rules making school meals healthier should be changed. The programs will continue even if the law expires, as long as congressional spending bills provide the dollars.

According to the Agriculture Department, one program will be shut down by expiration — the USDA National Hunger Hotline, which helps hungry people find local food resources.