NASHVILLE (AP) — Opponents to a Tennessee law requiring women to wait 48 hours before getting an abortion argue that such restrictions help perpetuate negative stereotypes about gender.

The argument is part of a lengthy lawsuit challenging the legality of the waiting period rule, which Tennessee's GOP-controlled Statehouse passed in 2015.

"The act thus violates the Equal Protection Clause by restricting women's ability to make autonomous, voluntary decisions concerning their reproductive lives and their medical care, while no such restrictions are imposed on medical decision-making by men," attorneys wrote on behalf of Planned Parenthood and other women's health clinics in an Aug. 16 pretrial brief.

The case is moving forward as Tennessee lawmakers are looking to join national efforts to enforce even stricter abortion restrictions despite warnings from critics that such actions will likely not pass legal muster. Republicans have recently tossed around proposals to ban abortions as soon as a woman knows she is pregnant, but such efforts have faced pushback among legislative leaders concerned about the costs of defending such a law unsuccessfully in court.

Currently, 34 states require women receive counseling before an abortion and 27 states require women to wait a specific amount of time, according to the Guttmacher Institute — a think tank that supports abortion rights. Only eight states, including Tennessee, prolong the waiting period longer than 24 hours.

After years of slowly navigating through the legal system, the Tennessee case is scheduled to go to trial in federal court in September.

"As plaintiffs will show at trial, requiring women seeking abortions to first receive certain state-mandated information and then undergo a mandatory, state-imposed delay discriminates on the basis of sex and sends the message that women are not competent, capable decision-makers," the brief continued.

Meanwhile, the state argues the ban allows women to have enough time make a competent decision over whether to have an abortion.

"The waiting period furthers the state's interest in protecting fetal life by offering prospective abortion patients an opportunity to make a different choice," wrote Republican Attorney General Herbert Slatery III in the state's pretrial brief filed the same day as the plaintiffs. "Both the Supreme Court and this Circuit have made it clear that waiting period laws will be upheld so long as they do not unduly burden a woman's right to terminate her pregnancy."

In 2015, former GOP Gov. Bill Haslam signed into law a series of new abortion restrictions. The first required women seeking abortions to get in-person counseling from a doctor and then wait at least 48 hours before being able to receive the procedure. The second required abortion clinics to be certified as outpatient surgery centers. The bills were enacted just a few years after Tennessee told doctors performing abortions that they must have admitting privileges at local hospitals.

Those Tennessee laws immediately faced lawsuits but the litigation was put on hold as the U.S. Supreme Court considered a separate challenge in Texas regarding admitting privileges and surgery center certification requirements. The high court eventually ruled such requirements were illegal.

Now, opponents are hoping for a similar result surrounding the waiting periods.