More than 500 state legislators from 50 states filed a brief with the Supreme Court of the United States last week, defending the expansion of Medicaid under the Affordable Care Act (ACA).

The ACA requires states to cover individuals and families with incomes up to 133 percent of the federal poverty level in their Medicaid plans starting in 2014, a provision that is expected to result in a significant increase in Medicaid enrollment. The provision has been targeted by the 26-state lawsuit that seeks to overturn major portions of the federal health-care reform law.

In an amicus brief, 539 largely Democratic state legislators affiliated with the Working Group of State Legislators for Health Reform, and in partnership with the Constitutional Accountability Center and the Progressive States Network, outlined their legal defense of the Medicaid expansion.

According to a summary released by the Progressive States Network, the ACA includes federal assistance for states to manage the expansion, that the reform of the health-care system is vital to the American public and that the expansion of Medicaid is crucial to extending insurance coverage to currently underserved citizens.

The Supreme Court is scheduled to hear arguments on the ACA’s constitutionality on March 26, 27 and 28.