Quebecor sent a lawyer's letter to the CBC last week demanding it retract the online statement, and post both an apology and a copy of a Quebecor press release.
The media conglomerate said the CBC had published "false and defamatory" material and that it had done so maliciously.
But the CBC sent its own lawyer's letter to Quebecor on Thursday arguing its commentary was not false, defamatory nor malicious. It is refusing to retract or apologize for the statement.
"Consequently, be advised that any process that your client intends to undertake against the CBC or its representatives will be judged groundless and will be vigorously contested," wrote CBC lawyer Sylvie Gadoury.
There has been long-standing tension between the two rival broadcasters, but it has peaked in recent weeks as a House of Commons committee studies the CBC's record on access to information and its dispute with the information commissioner in the courts.
Quebecor's media outlets, including the SunNews Network, the QMI news service and Sun newspaper chain, have published and broadcast regular stories and commentary critical of the CBC, particularly its approach toward access to information.
CBC President Hubert Lacroix has accused Quebecor publicly of trying to weaken the CBC to further its commercial position. The two companies compete head-to-head for viewers in Quebec.
The CBC's original volley, published on its website Oct. 19, was titled "What Quebecor won't tell you about its attacks on the public broadcaster." It appeared the day before Quebecor President Pierre Karl Peladeau appeared at the Commons access committee.
Quebecor's lawyer Bernard Pageau sent a letter to the CBC on Oct. 21, taking issue with the suggestion that Quebecor was hiding facts from the public and not telling the truth in its reports or in its public appearances.
The CBC statement said that Quebecor had received more than half a billion dollars in direct and indirect subsidies from Canadian taxpayers over the last three years — something Quebecor also said was a false and unverified assertion.
The CBC said its rival was using its newspapers and SunNews TV licence to pursue a "campaign against CBC-Radio Canada."
"No smear campaign led by Quebecor exists," wrote Pageau.
"Quebecor is a media company that is exercising its press freedom by informing the public on all sorts of questions of public interest as it has the right and fundamental freedom to do under the Charter of Rights and Freedoms."
The CBC countered this week by saying that a review of media coverage in Quebecor's newspapers and TV reports backs up its assertions.
"The title alone of a series of report, 'CBC Money Drain,' demonstrates our case," Gadoury wrote.
The CBC's original release also said Peladeau had sent more than a dozen letters to Prime Minister Stephen Harper and other officials to complain that the Crown corporation isn't spending enough money advertising in Quebecor newspapers.
Quebecor also said that statement was false, but added that it had been the subject of an unfair boycott by the CBC.