Fox News chief Roger Ailes said any political candidate who blacklists a news organization is making a "terrible mistake."
His remarks followed Democratic presidential hopeful John Edwards' decison to skip a Nevada debate co-hosted by Fox News.
Liberal activitsts say the news channel has a conservative bias and are urging Democratic presidential candidates to boycott the debate, which is also sponsored by the Nevada Democratic Party.
"Any candidate for high office from either party who believes he can blacklist any news organization is making a terrible mistake about journalists," Ailes said.
Ailes, who did not mention Edwards by name, spoke at a Radio and Television News Directors Foundation dinner in Washington on Thursday night.
"Recently, pressure groups are forcing candidates to conclude that the best strategy for journalists is divide and conquer, to only appear on those networks and venues that give them favorable coverage," Ailes said.
Ailes said that candidates "who cannot answer direct, simple, even tough questions from any journalist runs a real risk of losing the voters."
Earlier this week, Edwards' campaign said the involvement of Fox News was part of the reason the candidate was passing on the Aug. 14 debate in Reno.
Online activists and bloggers quickly hailed Edwards' decision as a victory in their campaign to urge Nevada Democrats to drop Fox News as a partner.
MoveOn.org Civic Action says it has collected more than 260,000 signatures on a petition that calls the cable network a "mouthpiece for the Republican Party, not a legitimate news channel."
The two Democratic presidential frontrunners, Sen. Hillary Clinton and Sen. Barack Obama, have not indicated whether they will attend the Nevada debate. Fox boss Rupert Murdoch threw a Senate fundraiser for Clinton, and is said to have a good relationship with the former first lady.
Democratic Party officials and Senate Majority Leader Harry Reid initially touted the partnership with Fox News as an opportunity to reach out to a different bloc of voters.
But in a letter posted Wednesday on the party's Web site, Democratic Party Chairman Tom Collins said Reid now shares activists' concerns and "has asked us to take another look."
Collins said the party would invite a "local progressive voice" to participate on the debate panel, which also would include a reporter from a local Fox affiliate, a national Fox News reporter and the moderator.
The party also invited the local Air America affiliate, a liberal radio network, to air the event live. C-SPAN will carry the debate after the Fox News broadcast and PoliticsTV.com to carry the live Fox News webcast feed on its site for one-time viewing, he said.
MoveOn Civic Action spokesman Adam Green dismissed the offer as "a lame proposal that would have multiple Fox personalities joined by one lone Air America panelist. That's a rigged, unfair and unbalanced debate."
"The Fox debate should just be canceled and a more legitimate news source should be found," Green said.
Nevada Democratic Party spokeswoman Kirsten Searer said Edwards is the first candidate to formally respond to the invitation. New Mexico Gov. Bill Richardson has said publicly he plans to attend.
Searer said the decision to partner with Fox, which will pay for some production and promotion costs, is part of Nevada Democrats' overall plan to bring new voters into the presidential process and its new early caucus, scheduled for Jan. 19.