Starboard Value has written a letter to Staples urging it to merge with rival Office Depot, potentially setting the stage for the activist investor to pursue a proxy contest several weeks from now. In December, Starboard revealed it had taken a 6.1 percent stake in Staples and increased an existing stake in Office Depot to 9.9 percent. At the time, CNBC reported that Starboard was pursuing a merger but the investor hadn't made its intentions public until now.