The U.S. Supreme Court on Monday opted not to hear an appeal filed by Lockheed Martin Corp., which was contesting a class action lawsuit brought by employees.

The company wanted the court to throw out the lawsuit filed on behalf of potentially 56,000 employees. The lawsuit claims that Lockheed is liable for poor management of its employee retirement plan under the federal U.S. Employee Retirement Income Security Act.

The case, originally filed in 2006, will now return to an Illinois federal court for further proceedings.

Previously, a federal judge said the lawsuit did not meet the requirements to proceed as a class action, but in an August ruling, the 7th U.S. Circuit Court of Appeals threw out that decision.

Lockheed then sought Supreme Court review on a threshold issue of whether any of the named plaintiffs had shown they had been harmed. The company said that at the time of the lawsuit, only one of the named plaintiffs, Lloyd DeMartini, had invested in the fund at issue and that it had been performing well during the time he was participating.