A major shareholder in Macrovision Corp. said it plans to vote against Macrovision’s proposed acquisition of Gemstar-TV Guide International Inc. because it’s too risky for the software company.

Loeb Partners Corp., which owns a 2.1 percent stake in Santa Clara-based Macrovision, said in a statement that the proposed $2.8 billion acquisition of Los Angeles-based Gemstar “introduces leverage and substantial execution risk.”

The $6.35 per share price represents a 6.2 percent premium on Gemstar’s closing price the day prior to the announcement and a 25 percent premium before Gemstar announced it was exploring strategic alternatives in July. Gemstar’s board has already approved the deal.

Shareholders in both companies have shown their disapproval of the deal, sending shares in Macrovision down nearly 40 percent since the acquisition was announced Dec. 7. Shares in Gemstar had shed as much as 27 percent since the announcement.

Gemstar shares were flat at $4.71 in afternoon trading Thursday on the Nasdaq.