The famed raider is seeking three seats on Biogen Idec’s board, the biotech disclosed this morning. The move raises the specter of a proxy fight and, perhaps, causing Biogen to again be up for sale. The biotech was unable to find a buyer and last month ended an auction, despite interest from several large drugmakers, partly due to a huge run-up in its stock price after Icahn’s initial investment became known.

In a research note this morning, Geoff Meacham, an analyst at JP Morgan, wrote that he expects “volatility in Biogen’s shares, given what looks to be a looming proxy fight with the potential outcome of reopening the auction process that was initiated last fall,” according to Reuters.

Icahn is proposing the nomination of three candidates to Biogen’s board: Alexander Denner, managing director of Icahn Partners; Richard Mulligan, professor of genetics at Harvard Medical School; and Anne Young, head of neurology services at Massachusetts General Hospital. Denner and Mulligan are also on the board at ImClone Systems, which overhauled its management after a heated battle with Icahn.