The Santa Monica-Malibu school district and environmental activists are going to trial, opening a new chapter in a protracted and bitter dispute over chemical testing and cleanup at Malibu schools.

A lawsuit filed against the district by two advocacy groups last year is expected on Tuesday to reach the U.S. District Court for the Central District of California in Downtown Los Angeles.

Malibu-based America Unites for Kids and Washington, D.C.-based Public Employees for Environmental Responsibility are seeking the removal of polychlorinated biphenyls, which were discovered in the caulking at Malibu campuses more than two and a half years ago. The plaintiffs have repeatedly criticized the district for spending millions of dollars on consultants and legal fees instead of replacing the contaminated building materials.

“We are committed to … exposing the truth about PCBs in Malibu schools and putting officials across the country on notice that parents will not stand for their kids being poisoned in their classrooms,” said America Unites leader Jennifer deNicola, a Malibu parent. “Public health should be their top priority.”

The district, meanwhile, contends that it continues to comply with remediation guidelines set by the federal Environmental Protection Agency. The district maintains that the EPA’s guidance is consistent with the views of scientists and health experts.

“The District is confident that once the full extent of its compliance with EPA’s policy and requirements, as well as the pending modernization schedule for Malibu High School and Juan Cabrillo Elementary School, are before the Court, a proper decision will be reached,” SMMUSD spokeswoman Gail Pinsker said in a statement.

The trial arrives more than a year into a fierce legal battle that has fueled ongoing efforts by some Malibu parent groups to create a separate school district.

In March 2015, America Unites and PEER filed a lawsuit against Superintendent Sandra Lyon, chief financial officer Jan Maez and all seven Board of Education members over the district’s handling of chemical testing and cleanup at Malibu schools. About two months later, a request by SMMUSD officials to dismiss the suit was denied.

By October, the district was seeking criminal vandalism charges against deNicola after she collected independent caulk samples and provided the district with additional PCB testing results. The alleged crimes were reported to the county Sheriff’s Department, but the county District Attorney’s Office declined to file criminal charges.

SMMUSD then pursued court-ordered sanctions that were imposed on the plaintiffs in December. The activists will not be allowed to use the samples they obtained as evidence in the lawsuit, and they were instructed to pay for repairs related to damage from deNicola’s unauthorized testing.

In March, the court paved the way for a trial when it denied the district’s motion for summary judgment. The court concluded that “evidence suggesting that the District has failed to implement and consistently employ [best management practices] as contemplated by the EPA’s approvals calls into question the amount of deference the Court should give to the District’s purported compliance with the EPA’s guidelines and approvals.”

The trial is expected to begin three days before a May 20 gala for American Unites hosted by model Cindy Crawford, who pulled her children out of Malibu public schools amid concerns over PCB-related health risks.