Taking its bid to buy Yahoo! to a new level, Microsoft has threatened to take its offer directly to the shareholders of the Internet giant and hinted even at a proxy contest for a new board, if an agreement is not reached within the next three weeks.

In a letter to the Yahoo! board of directors, Microsoft Chief Executive Steve Ballmer said by choosing not to enter into substantive negotiations with us, you have failed to give due consideration to a transaction that has tremendous benefits for Yahoo!’’s shareholders and employees. Meanwhile, a source said Yahoo’’s board is expected to discuss Ballmer’’s letter next week, as well as provide a briefing on how talks between the two firms went last week.In addition, Microsoft also threatened to lower its existing bid if the deal is not done by April 26. “If we are forced to take an offer directly to your shareholders, that action will have an undesirable impact on the value of your company from our perspective which will be reflected in the terms of our proposal,” wrote Ballmer.

Microsoft had offered an unsolicited buyout bid of $31 per share for Yahoo! on February 1.The Internet giant rejected Microsoft’’s initial offer saying that it was too low and undervalued the company.