GM rejected Greenlight's plan in March to appoint three directors to GM's board and divide the common stock into two classes. Now the hedge fund's newly launched website, UnlockGMValue.com, calls for investors to "VOTE GREEN CARD TODAY."
GM's annual shareholder meeting is scheduled for June 6. GM said in a statement that Greenlight's proposal "creates an unacceptable level of risk."
Shares of the automaker fell about 1.5 percent in midday trade and are down more than 5 percent this year.
Website landing page
The proposal "would unlock tens of billions of dollars of shareholder value and was specifically designed not to change GM's business strategy, capital allocation priorities or financial policy," according to the website.
Greenlight owns 3.6 percent of GM common stock, making it the fifth largest public shareholder of the auto manufacturer.
The hedge fund returned just 1 percent in the first quarter, trailing the S&P 500's 6 percent gain, according to the hedge fund's letter sent to shareholders last week.