The Green Party is considering legal action against the BBC for giving comparatively more airtime to TUV during the Assembly election campaign despite it having fewer MLAs.
The party has submitted formal complaints to the BBC and broadcast regulator Ofcom and has launched an online petition.
TUV leader Jim Allister was the party's sole MLA before Stormont was dissolved ahead of May's election.
The Greens had two MLAs - party leader Clare Bailey in South Belfast and North Down's Rachel Woods.
However, TUV received marginally more first-preference votes in the last Assembly election in 2017 with 2.6% compared to 2.3% for the Green Party.
And some opinion polls in recent months have suggested an increase in TUV support due to a split in the unionist vote.
Ms Bailey accused the BBC of choosing "division and sensationalism" against the Green Party's "real alternative to the traditional parties' politics of division".
She said: "Our public service broadcaster has a duty to be impartial, especially during an election campaign.
"However, the BBC has decided to grant the smaller TUV more coverage than the Green Party NI, including giving them an extra Party Election Broadcast.
"In the most recent elections, the Green Party NI won more Assembly and local council seats than the TUV, so it makes no sense for the BBC to treat the TUV as a bigger party than the Greens.
"In no other democracy would the main opposition party be excluded from election debates and other election coverage.
"We have submitted formal complaints to the BBC and Ofcom, and the Green Party NI is actively considering its legal options."
Ms Bailey urged members of the public to sign a petition on the party's website to show they are "opposed to the distortion of our democracy".
A BBC spokesman said: "We have a careful and detailed process in place for how we make judgments about the coverage of parties during election periods.
"This takes account of relevant Ofcom requirements and the BBC's own election guidelines."
A TUV spokesman also said the coverage afforded to the party as it stands does not reflect "our level of support".
"The coverage TUV is reviving in the broadcast media is dictated by policy papers set by broadcasters long before the election," he said.
"The surge in support for TUV, demonstrated in both a vastly increased membership and many opinion polls, is a matter of public record.
"This is because the people recognise and appreciate the stand TUV has taken in relation to the Northern Ireland Protocol.
"TUV would argue that the coverage afforded us during the campaign by broadcasters does not truly reflect our level of support.
"Recent polls have shown support for TUV above that demonstrated for Alliance before the last election and yet they were included in the main leaders' debates while TUV will be excluded."
Read more: Every candidate running for the Stormont Assembly
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