When federal lawmakers planned the massive expansion of Medicaid as part of the Affordable Care Act, they included a big enticement to physicians — a significant, but temporary, pay increase.

Although the pay increase was not tied to Medicaid expansion, New Jersey accepted the deal. Some 300,000 additional state residents have enrolled in Medicaid in the last year.

Even though the number of patients continues to increase, come Jan. 1, the pay increase will be gone, adding even more stress to overburdened health care providers in the state.

The provision of the health law that boosted Medicaid reimbursement rates to make them equal to Medicare rates expires at the end of the year.

Medicaid reimbursements to New Jersey providers will decline by 53 percent, according to an Urban Institute report. Only four other states — New York, Michigan, California and Rhode Island — will see greater decreases, the report found.

Because the state has had a low reimbursement rate, only about 40 percent of New Jersey physicians accept Medicaid patients — a nationwide low, according to a 2012 Health Affairs study.

In addition, because many feared the boosted payments would end without an extension, few of the state's doctors who hadn't been accepting Medicaid patients joined the program, she said.

"Many doctors in New Jersey didn't trust that it would be a long-lasting parity situation," said Campagnolo, a past president of the Medical Society of New Jersey.

Medical society CEO Lawrence Downs speculated in a Nov. 18 letter to Human Services Commissioner Jennifer Velez that the return to 2012 reimbursement levels could drive physicians out of Medicaid.

"Our concern is that we could have 5,000 less physicians accepting Medicaid in 2015, when payments go back down to one of the lowest in the nation," he wrote. "Thus, continuation of this payment level is crucial for the proper access to care for Medicaid patients."