LITTLE ROCK — A southwestern Arkansas physician who is a convicted sex offender has filed a federal lawsuit challenging a new state law that prohibits registered sex offenders from providing Medicaid-funded services in the state.

Dr. Lonnie Joseph Parker argues in the lawsuit filed Friday that the new law, which took effect Aug. 16, violates his constitutional rights.

Parker, who practices in Hope, said in the lawsuit that he provides emergency and general family medical services — including family planning — to rural poor in the state and is a registered provider under the Arkansas Medicaid Program. More than 75 percent of his patients are Medicaid beneficiaries, he said.

Parker was joined in the lawsuit by patients who want him to continue being their family primary care doctor, including Tonya Witherspoon, a mother of five and a Medicaid recipient, and Paula Sunderman and her daughter, Sara.

The law seeks a preliminary injunction to halt enforcement of the law pending the outcome of the lawsuit.

In 2000, Parker was convicted of possessing pornography and sentenced to 49 months in prison. He is classified by the Arkansas Sex Offender Assessment Committee as Level 1 sex offender, the lowest level.

In the lawsuit, Parker argues Act 1504 of 2013 "inflicts punishment on a specific group of individuals without judicial trial" in violation of his constitutional right, and "imposes retroactive punishment" because his conviction was more than 10 years ago.

The lawsuit also alleges Act 1504 violates the rights of his patients by denying their "right to choose any willing, qualified health care provider under the Medicaid program," and excludes "Medicaid providers for reasons unrelated to their qualifications."

Senate Bill 984, which was later signed into law as Act 1504, was filed by Sen. David Sanders, R-Little Rock, after a legislative audit of Arkansas’ Medicaid program revealed that Parker had received more than $489,000 in Medicaid payments from 2009 to 2012.

The legislation was among a number of Medicaid reform bills adopted by the Legislature this year.