Bayrou said the conservative leader from the UMP party had used his media contacts to try to stop him from holding a televised debate with the socialist hopeful.
Sarkozy called the accusations insulting and his campaign director, Claude Gueant said Bayrou was using "Stalinist" tactics.
"It's slander, a slanderous insinuation," he said.
Despite finishing third in last Sunday’s first round vote, Bayrou has remained a key figure in the presidential campaign as both Royal and Sarkozy have been courting the 6.8 million constituents who voted for him in the first round.
Royal has narrowed the gap on the frontrunner Sarkozy but still trails in recent surveys, making it vital for her to appeal to Bayrou's centrist followers.
A TNS Sofres poll this week showed 46 percent of Bayrou's voters support Royal, against 25 percent for Sarkozy and 29 percent who have yet to make up their minds. Other polls however have showed support roughly evenly split.
Royal is keen to use Saturday's debate to highlight the values she shares with Bayrou and attract moderates who may consider voting for Sarkozy but are also worried by his image as a hardliner.
Bayrou has refused to endorse either candidate or publicly engage in any political deal but made clear his antipathy to Sarkozy by telling RTL radio he was sure his former ally wanted to silence his opponents.
|Despite his defeat Bayrou is still |
managing to get plenty of TV time [AFP]
"I say with certainty that we have before our eyes today the proof of this propensity or choice of Nicolas Sarkozy to control the news and debate, and this is harmful for France," he said.
Bayrou has campaigned against Sarkozy's links to big business and media groups, notably the TF1 station owned by Martin Bouygues, a close friend of Sarkozy, who runs the media, construction and telecommunications conglomerate Bouygues.
Royal said: "I think all the pressure that has taken place, notably within a media-financial system to which Nicolas Sarkozy is very linked, have no reason to exist in a democratic country where freedom of speech and debate is very important."
"I'm today holding out my hand ... to all those who think that human values must always prevail over financial and market values," she told supporters at a rally in Lyon.
Sarkozy vehemently denied any involvement in CanalPlus deciding not to air the debate and accused Royal and Bayrou of trying to stage the "Moscow trials", in reference to the show trials of Stalin's political opponents in the 1930s.
"No one is under control, no one is putting pressure," Sarkozy said during a campaign swing in the central French town of Puy Guillaume.
"If renewing politics means staging Moscow trials like this one, this is not renewal," said Sarkozy, the 52-year-old candidate of the governing party.
Sarkozy has said voters were more interested in a debate between the two finalists scheduled for Wednesday.
"I will allow no-one to continue to insult and slander me," he later told a rally in the town of Clermont-Ferrand.