BP Plc was sued by members of its employee savings plan over losses tied to the company’s plunging stock price amid the oil leak disaster in the Gulf of Mexico.

BP has lost more than half of its market value since the April 20 explosion that caused the largest oil spill in U.S. history. The fire and blast aboard the Deepwater Horizon drilling rig that was working on a well for London-based BP killed 11 members of its crew.

The lawsuit, for which the workers are seeking class- action, or group, status was filed yesterday in federal court in Chicago.

“Defendants knew or should have known that investment in BP Plc equity was -- and continues to be -- an imprudent investment of the ESP’s assets due to serious mismanagement and improper business practices that resulted in catastrophic incidents of international significance, including, among others, the BP spill in the Gulf of Mexico,” the plaintiffs claimed.

Full-time, part-time, occasional and temporary employees are eligible to invest in the employee savings plan, or ESP, according to the lawsuit. Regulatory filings show that the plan held $2.45 billion worth of BP American depositary shares, or 29 percent its $8.27 billion of assets, at the end of 2009, according to the complaint.