Yahoo called Microsoft's threat of a hostile takeover "counterproductive" on Monday, while also saying it is open to a deal but only at a higher price.

In a letter addressed to Microsoft CEO Steve Ballmer, Yahoo's CEO Jerry Yang and Chairman Roy Bostock said Microsoft has mischaracterized the negotiations since the initial offer was made, and that the two companies have had "constructive conversations."

"We consider your threat to commence an unsolicited offer and proxy contest to displace our independent board members to be counterproductive and inconsistent with your stated objective of a friendly transaction," the letter said.

Yahoo said Microsoft's falling stock price has devalued the value of the proposal. Microsoft offered Yahoo a cash-and-stock deal worth $44.6 billion.

Yahoo also said Microsoft has not responded to requests for more information on antitrust issues since a deal would be subject to regulators.

"To date, you have still not provided any of the requested information," the letter said.

The IDG News Service is a Network World affiliate.