Fine Gael members were told RTE was "institutionally opposed" to the Government and the station "orchestrated attacks" on former tanaiste Frances Fitzgerald to "destroy her political career".
The comments were made in a briefing to Fine Gael members in Dun Laoghaire by the constituency's director of elections Paddy Hayes.
Mr Hayes told General Election canvassing teams they would get "no favours" from the "cynical national media", which is opposed to giving Fine Gael a "fair crack of the whip".
"RTE is institutionally opposed to [the] Government. This applies to RTE news and current affairs in particular. You only have to listen to the curled lips of the presenters any time a Fine Gael representative is on air to see that," he said.
"Who can forget that RTE orchestrated attack on Frances Fitzgerald as they set out to destroy her political career?" he added.
The comments by the senior party member came as Taoiseach Leo Varadkar and Fianna Fail leader Micheal Martin prepared for their first head-to-head leadership debate on Virgin Media tomorrow night.
The two party leaders will also face off against each other in a televised debate on RTE during the final week of the campaign.
Mr Varadkar said he was looking forward to "demonstrating some of the weaknesses" in Fianna Fail's policies.
He said the public would be focused on the head-to-head debates rather than the ones involving all party leaders.
Mr Martin said the debates would be "challenging" but added he was looking forward to taking part.
Sinn Fein's director of elections Pearse Doherty has written to Virgin Media objecting to the proposed debate.
Mr Doherty said there was "no substantial difference" between Fine Gael and Fianna Fail and insisted Sinn Fein party leader Mary Lou McDonald should not be excluded.
Sinn Fein has also objected to RTE, the State-funded national broadcaster, excluding its party leader from a separate debate.
The row over televised debates comes after Fine Gael issued a statement calling on Fianna Fail to "stop attacks on media".
In the statement, Fine Gael parliamentary party chairman Martin Heydon said the "first instinct" of Fianna Fail representatives was to "attack the media for legitimate scrutiny".
"It is simply wrong that the Irish media is attacked by Fianna Fail for doing their job," he said.
"I would respectfully suggest the Fianna Fail leadership take a moment of self-reflection before attacking our media again."
However, in his briefing to supporters, Mr Hayes said it was a "fact" that most people working in the media were "instinctively left wing, pro the unions, naturally sympathetic to the Shinners, Coppinger, Boyd-Barretts and their ilk".
"Even the Irish Times, which used to walk the middle ground, has been largely captured by the left," he added.
A Fine Gael spokesperson said the party "zealously encourages a free press, free exchange of views and objective, forthright examination of all political parties".
An RTE spokesperson said: "Under the Broadcasting Act 2009, RTE fulfils its obligation to provide fair, objective and impartial coverage. We are also accountable to the BAI."
Mr Hayes did not respond to requests for comment.
Meanwhile, Fianna Fail is seeking an investigation by the State's ethics watchdog into Fine Gael's use of State funding and Government events during the election campaign.
The party's public expenditure spokesperson Barry Cowen said he plans to write to the Standards in Public Office Commission to request an immediate investigation into an event involving the Taoiseach and Apple chief executive Tim Cook.
Mr Cowen said the Taoiseach used the event at the National Concert Hall, organised by the Irish Development Authority (IDA), to directly attack Fianna Fail and other opponents.
Mr Varadkar criticised opponents of the National Broadband Plan at the event.