April 2 (Bloomberg) — Two former McDonald's Corp. store managers, assisting with a campaign to raise pay for fast-food workers, said they helped withhold employees' wages at the restaurant chain after facing pressure to keep labor costs down.

The ex-managers, who came forward as part of an effort backed by worker advocacy group Fast Food Forward, said they engaged in tactics such as asking employees to continue working after they clocked out or adding unpaid breaks to time sheets. They took the steps to avoid exceeding a store's strict goals for wage expenses, said Lakia Williams, a former assistant manager at a McDonald's in Charleston, South Carolina.

"There was so much pressure," she said in an interview. "It's not only the franchisees group and the general managers, it is corporate. It's something internal, it's something deeper, and it's something that has been going on for years."