The Wall Street Journal has news that a person familiar with the Microsoft bid of Yahoo knows that Yahoo Inc.’s board plans to reject Microsofts unsolicited $44.6 billion offer to acquire the Web giant.

After a series of meetings over the past week, Yahoo’s board determined that the $31 per share offer “massively undervalues” Yahoo, the person said. It also doesn’t account for the risks Yahoo would be taking by entering into an agreement that might be overturned by regulators. The board plans to send a letter to Microsoft Monday, spelling out its position.

Yahoo’s board believes that Microsoft’s is trying to take advantage of the recent weakness in the company’s share price to “steal” the company. The decision to reject the offer signals that Yahoo’s board is digging in its heels for what could be a long takeover battle. The company is unlikely to consider any offer below $40 per share.

It’s unclear as of yet whether Microsoft would be willing to pay such a premium, which would increase the value of its original cash and stock bid by more than $12 billion but the rejection comes as Yahoo’s board has been considering various other scenarios, including a search advertising partnership with Google.