McDonalds Corp. (NYSE:MCD) found itself back in activist investor Bill Ackman's crosshairs after the company's move to reduce its holdings in Chipotle Mexican Grill through a stock swap. The company disclosed in an 8-K filing earlier today that Ackman's Pershing Square Capital Management would increase their McDonald's common stock holdings by almost $800 million after the swap.

Last year, Ackman pressured the company to spin off 65% of their owned restaurants in a stock offering, but backed off after McDonalds agreed to $1 billion stock buyback and other measures designed to increase shareholder value. Ackman's fund was also actively involved with Wendy's (NYSE:WEN) restructuring, which included the spin off of their Tim Horton's (NYSE:THI) chain. With these new shares, many investors are speculating that the activist investor will step in again to encourage the company more actively unlock shareholder value.

Whether this materializes or not, when an activist hedge fund discloses an $800 million stake in the company it's something worth watching closely.

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