THURSDAY, March 22 (HealthDay News) -- The Medicaid program is bracing for an expansion that will bring an estimated 16 million more Americans into the health-care safety net, as required by the Affordable Care Act.

But whether that happens depends on how the U.S. Supreme Court rules on the legal challenges to the massive health-care reform legislation.

Twenty-six states are challenging the requirement to comply with the new Medicaid eligibility rule or lose federal matching funds, calling it coercive and a violation of states' rights. On March 28, they will argue before the Supreme Court that that provision of the Affordable Care Act is unconstitutional.

The Medicaid expansion opens eligibility to all people with household incomes up to 133 percent of the federal poverty level -- whether unemployed or the so-called working poor -- starting in January 2014. That translated into an annual income of approximately $14,850 for an individual and $30,650 for a family of four in 2012, according to the U.S. Department of Health and Human Services.

Until now, the main groups of people served by the Medicaid program have been low-income parents and children, the frail elderly and the disabled.

The Medicaid expansion provision is considered more likely to survive the legal challenge than the Affordable Care Act's most controversial provision: the individual mandate, which requires most adults to have health insurance or pay a fine.

"I don't think [the Medicaid expansion] is as vulnerable, but it isn't an entirely trivial issue. The basic point is that the [U.S. Supreme] court has been very clear for a very long time that Congress can require states to do things using Congress' spending power," said Renee M. Landers, a professor at Suffolk University Law School in Boston.

"The problem the challengers have in [arguing] that the [Medicaid expansion] is coercive is that the federal government is paying for 100 percent of the expansion for the first 10 years that the law is in effect," Landers said.

On Feb. 17, a group of 12 state attorneys general filed a brief in support of the expansion's constitutionality.

"In a cooperative federalist program, the federal government establishes the program's core requirements and gives the states the freedom to implement their own programs within those requirements," an excerpt from the brief states.

At least five states are expanding their Medicaid programs early: California, Connecticut, Minnesota, New Jersey and Washington, along with Washington, D.C. Illinois is planning an early expansion as well.

Will there be enough doctors to handle Medicaid patients?

Some physician groups are concerned about the effects of a massive influx of enrollees into the already-strained Medicaid system.

Shortages of doctors already exist in specialties most likely to work with Medicaid patients -- such as pediatricians and family practitioners. And doctors say current Medicaid reimbursement rates from government are too low to encourage more doctors to treat Medicaid participants.

"While expanding Medicaid access to more low-income Americans under the Affordable Care Act was an important step in the right direction, more progress is needed," said Dr. Peter Carmel, president of the American Medical Association. "Most physicians are currently unable to accept Medicaid patients due to low reimbursement rates, and this problem must be addressed as new patients enter the program."

One opponent of the Affordable Care Act said expansion of the Medicaid program would hurt current enrollees by reducing access to health-care providers and forcing longer waiting times -- without helping the newly eligible.

"Medicaid may give them insurance cards -- good luck getting that care," said Grace-Marie Turner, president of the conservative Galen Institute.

Dr. Glen Stream, president of the American Academy of Family Physicians, cited parts of the new law that, he said, should attract and train more physicians in settings that serve Medicaid patients.

"Components like teaching health centers are part of the Affordable Care Act," he said. "That's to take a federally qualified health center and do medical residency, medical education in that health center."

And he said a provision for student loan forgiveness could help overcome a barrier to medical students choosing family medicine and other primary-care specialties.

"It's important to acknowledge for our membership that [the new law] was controversial," Stream said. "We have 100,000 members across the country and certainly they represent the political diversity in our society.

"Our academy is focusing -- because the Affordable Care Act is now law -- on helping to preserve and expand and implement those pieces that we see as important to the health of people in our country," he added.

More information

To learn about the Affordable Care Act and Medicaid eligibility, visit Medicaid.gov.

To read an overview story on the Affordable Care Act, click here.

For legal experts' best guess on how the Supreme Court will rule on the Affordable Care Act, click here.

To learn more about the importance of the individual mandate to the Affordable Care Act, click here.