Internet search engine Yahoo says it is "not opposed" to Microsoft's takeover bid, but wants a better price.
The letter from Yahoo's board was a swift response to a deadline issued at the weekend by Microsoft CEO Steve Ballmer for Yahoo to agree to the deal.
Microsoft warned if the deal was not accepted by 26 April, it would mount a hostile takeover at a lower price.
The software giant made an unsolicited $44.6bn (£22.3bn) takeover offer for Yahoo on 31 January.
But Yahoo rejected the deal, saying it substantially underrated the company's value and prospects.
Read more