Sinn Fein is considering legal action against Virgin Media over the decision not to let the party take part in tonight's leaders' debate with Fine Gael and Fianna Fail.
Party president Mary Lou McDonald described it as a "bad joke" that Sinn Fein has not been included in the programme, hosted by Pat Kenny, that will see Leo Varadkar and Micheal Martin go head to head.
Speaking after the most recent opinion polls put her party only two points behind Fine Gael, Ms McDonald said it was an issue of fairness and having a wide range of voices heard in the run-up to the election.
Deputy Pearse Doherty said he is looking into the issue and is calling on RTE to include Sinn Fein in its forthcoming debates.
"I've written to Virgin Media and we've already written to RTE about this decision. It's an issue of fairness," he said.
"We will be meeting with our legal team later and, as I said, we haven't heard from the station. We will consider all our options at that point.
"There is no obligation in terms of being under the Broadcasting Act, but this is about fairness.
"I don't think any TV station wants to exclude a large section of the population and the voices of that population.
"We have seen two opinion polls now that put us neck and neck with Fine Gael.
"There is no justification. People right across the political divide are saying this is unfair at this point in time.
"We do expect them to reverse this decision and, if they don't, we have to stand up for those voices which won't be heard, and it will be a sham debate if the voice of Sinn Fein isn't tabled."
Sinn Fein introduced its 42 general election candidates in 38 constituencies at an event at the Mansion House yesterday.
Deputy McDonald said it was "not fair to exclude voices such as ours" from the televised debate, and claimed the election should not be perceived as a two-horse race.
Speaking after the launch, she told reporters: "This is about having an open and fair debate in an open and democratic election. To us, it's a no-brainer.
"In fact, it will be a bad joke if you have two men who have been in government with each other for four years debating the big issues of the day.
"The last thing we want to be is on a collision course with any section of the media, but there's a moment to stand up for what's right, and it's just wrong to exclude people. It's a bad decision."
Ms McDonald also said at the Mansion House that she hopes to have a referendum on the unification of the island by 2025, saying Irish unity is "the best idea for the future of our country".
Virgin Media Television said in a statement that it will be offering viewers comprehensive coverage of the election across news and current affairs programmes and will be "fair and impartial" and in accordance with BAI guidelines.
It is allocating coverage throughout the general election 2020 campaign in proportion to parties' performances in the 2016 general election and the 2019 local elections.
The broadcaster said it is also hosting a multi-party leaders' debate on January 30 and a series of one-to-one interviews with the leaders of the main parties.