There has been a surge of class action lawsuits filed by workers seeking huge damages for back overtime based on claims that they were improperly classified as managers exempt from overtime laws. Now, more than 600 low-level managers have sued Robinsons-May Inc., a retailer with 46 department stores in California. The workers contend that although the company treated them as exempt, they were entitled to overtime pay. The lawsuit charges that during the employees’ typical 55-hour workweeks, they performed mostly non-managerial tasks, including stocking, working cash registers and cleaning up. Damages could top $18 million if the employees succeed. Robinsons maintains it complied with the overtime laws.