Zynga?s chief executive, Mark Pincus, got an earful from employees last month. In dozens of emails to a companywide list, frustrated workers complained about the long hours and stressful deadline periods. The quarterly staff survey solicited 1,600 responses, with plenty of criticism, including one person who said he planned to cash out and leave after the initial public offering.

Pincus took note, going through the comments and highlighting select excerpts. At a Zynga meeting several days later, he read some of the most acerbic words. Pincus said he was aware of the problems, but needed the staff?s guidance to fix them.

Few internet start-ups have grown as swiftly as Zynga, creator of a sprawling network of virtual farms, cities and poker tables that is preparing to go public.

Led by the hard-charging Pincus, the company operates like a federation of city-states, with autonomous teams for each game, like FarmVille. At times, it can be a messy and ruthless war. Employees log long hours, managers relentlessly track progress, and the weak links are demoted or let go.

But that culture, which has been at the root of Zynga?s success, could become a serious liability, warn several former senior employees who agreed to speak on the condition of anonymity because of fear of reprisals.

As the discord increases, the situation may jeopardise the company?s ability to retain top talent at a time when Silicon Valley start-ups are fiercely jockeying for the best executives and engineers. It could also hamper deal-making.

?Zynga should be an example of entrepreneurship at its best,? said Roger McNamee, a co-founder of the venture capital firm Elevation Partners. ?Instead it?s going to be a Harvard Business School case study on founder overreach ? this will be a cautionary tale.?