Zynga Inc filed with regulators for a secondary stock offering of up to $400 million on Wednesday, paving the way for some early investors to exit their holdings.

Shares of the online games maker, which have risen 33 percent since the company went public, rose marginally in premarket trading on Wednesday. They closed at $13.38 on Tuesday on Nasdaq.

In a filing with the Securities and Exchange Commission, Zynga said it is waiving the lock-up arrangement the company had with some of its existing stockholders to facilitate the offering.

Investors are typically expected to wait for about six months after an IPO to be able to sell their shares freely, in order to prevent volatility in a company's stock.

Zynga's lock-up agreements from its December IPO were to expire on May 28, 2012.

Zynga, which went public late last year in a high-profile IPO that raised $1 billion, said certain existing stockholders would sell class A shares of the company's stock.

It did not name the stockholders offering the shares, or the number of shares that will be sold.

Morgan Stanley and Goldman Sachs are acting as the lead underwriters for the offering.

(Reporting by Himank Sharma in Bangalore; Editing by Brenton Cordeiro)