This might complicate any attempt by an activist investor to pressure CEO Marissa Mayer to unload more of the Chinese e-tailer’s stock after its record-setting IPO last week. Yahoo still owns about 15% of Alibaba, about 383.6M shares, after selling 140M when it went Image (1) Yahoo_logo1__130822050504.jpg for post 720964public at $68 a share. Alibaba closed today at $90.57. But Yahoo says in an SEC filing today that it has a “lock-up agreement with the Underwriters restricting the sale of its remaining ordinary shares of Alibaba for a period of one year, subject to certain exceptions.” In addition, Mayer approved a voting agreement with Alibaba, its founder Jack Ma, Vice Chairman Joe Tsai and SoftBank Corp pledging to support directors nominated by SoftBank and Alibaba. Yahoo also gave Ma and Tsai a proxy to vote on any reduction of Yahoo’s Alibaba holdings.

Mayer is under the gun: Yahoo’s revenues have continued to decline despite splashy initiatives, including the hiring of former CBS anchor Katie Couric to be Yahoo News’ Global News Anchor. That has led to debates over how much, if anything, the company’s core media and Internet assets are worth. Pivotal Research Group’s Brian Wieser figures that Yahoo, which closed today at $39.88, is worth just a little more — $41 a share. And only $15 of that is attributable to its operations; the rest of the company’s value comes from the shares it owns in Alibaba and Yahoo Japan. Meanwhile, he says, “the direction the company will move in remains unclear.”