TV3's political show The Nation has excluded Mr Craig from the debate tomorrow morning, which will include New Zealand First, the Green Party, the Maori Party, Act, Mana and United Future.
Mr Craig's spokeswoman said he was seeking a last-ditch injunction to stop the programme from being broadcast unless he was included.
His lawyers were filing papers with the High Court this morning.
3 News said Mr Craig's party did not meet the criteria to take part in the debate.
A TV3 spokeswoman said tomorrow's leaders debate was focusing on parties which had been represented in Parliament in the last three years.
She said The Nation would not change the format as a result of Mr Craig's legal challenge.
The show was one of a series of political debates, and TV3 planned to invite the Conservatives to a future debate which would include all party leaders.
Conservatives won 2.6 per cent of the party vote in the 2011 general election – more than Maori, Mana, United Future or Act – but did not gain a seat
- Isaac Davison of the New Zealand Herald
