Glass Lewis & Co., a San Francisco-based shareholder advisory firm, has recommended that Six Flags Inc. investors vote Redskins owner Daniel M. Snyder and two others onto the board of the theme-park company.

The recommendation comes several days after Snyder said he had the support of owners of more than 57 percent of Six Flags' shares for his proposal to replace three board members with his hand-picked team. Six Flags and Snyder are awaiting an independent tally of the votes and certification of the result.

Shareholders can vote until around Dec. 24, and those who have backed Snyder can still change their minds.

Snyder, who has complained about the company's poor performance in recent years, wants shareholders to remove chief executive Kieran E. Burke, Chief Financial Officer James Dannhauser, and board member Stanley S. Shuman from the board of directors and to install himself, former ESPN executive Mark Shapiro and home builder Dwight C. Schar. Snyder wants to be chairman and have Shapiro become chief executive, but the board must approve management changes. Snyder, if the results are certified, would have only three seats on a seven-member board.

In its report, Glass Lewis criticized Six Flags for paying its managers more than competitors pay even though the company's performance was worse. The firm questioned the board's decision to put the company up for sale. It said that if a suitable buyer does not come forward, having Snyder's team on the board would lead to new management "with a substantial track record of creating value for shareholders" and "an eye toward accountability."

Two other shareholder advisory firms have already weighed in. Institutional Shareholder Services Inc. recently advised investors to back Snyder, while Proxy Governance Inc. said they should wait to see if a buyer comes forward.