Zynga, the online gaming company preparing for an initial public offering, thinks it may have been too generous with its stock.

The company regrets giving employees so many stock grants in its early days, according to a report in The Wall Street Journal. So it's telling some workers to give back some shares -- or get fired.

Zynga executives were concerned about creating a "Google chef" situation, the Journal reported. They were referring to the chef who joined Google (GOOG) in the early days and walked away with $20 million after the company went public.

Zynga makes the popular "Farmville" and "Mafia Wars" games, and could be looking at a valuation of $20 billion if its IPO goes well. Employees are sitting on a lot of money. In fact, some of them were sitting on as much as $200 million each, said one person close to the company, according to the Journal.

Chief executive Mark Pincus reportedly developed a hit list of employees whose work he thought didn't justify the large blocks of restricted shares they received when they were hired, according to the Journal.

Most of those aware of Zynga's demands for the return of stock said the effort was designed to replenish the pool of shares that could be awarded to attract new talent. One person called the effort part of Mr. Pincus's strategy to continually assess employees and create a meritocracy where the biggest rewards would go to biggest contributors, and nobody could just "rest and vest."