NASA will move to the Supreme Court to seek redress over the 2017 presidential election result.
Raila Odinga said they took the decision they had said they wouldn't to give the court a second chance. He said it also followed wide consultation and the current oppression on civil societies.
"The court can use this chance to redeem itself, or, like in 2013, it can compound the problems we face as a country," he told a press conference at the Okoa Kenya Secretariat in Lavington, Nairobi, on Wednesday.
Raila noted they will produce evidence of rigging in the election after which IEBC declared President Uhuru Kenyatta winner.
The Opposition was to make this announcement on Tuesday and the nation had been anticipating the release of "compelling evidence" that the presidential election result was rigged.
IEBC chairman Wafula Chebukati declared Uhuru the winner after he garnered 8,203,290 votes against Raila's 6,762,224.
But Raila said the National Super Alliance will not be part of a plan to turn the country into a "banana republic and playground".
He warned that if action is not taken, future elections will be a sham.
"We are giving the Supreme Court a chance to redeem itself from the 2013 judgement that favored Uhuru or compound the challenges into the days ahead. This is just the beginning...we will not accept and move on."
Raila accused Jubilee of assassinating IEBC ICT manager Chris Msando saying the intention of its leaders was to maintain power.
"Jubilee shamelessly cooked the results through non-existent forms 34A. An algorithm was put in place to manipulate original results keyed in," he added.
"The commission refused to address all the questions submitted by NASA and rather announced Uhuru president-elect though forms 34A had not be verified. We are not going to accept computer generated leaders until all our concerns are addressed."
Police and KRA authorities on Wednesday raided the office of AfriCOG, a pro-democracy organisation that had raised questions over preparations for last week's disputed election.
Lawyer Haron Ndubi blocked them and questioned the manner in which they stormed the premises.
"There is nothing wrong with AfriCOG petitioning election results," the lawyer also said. "Courts are there to listen for redress. President Uhuru Kenyatta has never been comfortable with NGOs because of the perception they took them to The Hague."
The Supreme Court threw out AfriCOG's petition after the March 4, 2013 general election.
The High Court later suspended the action.
Also read: High Court suspends Fazul action on AfriCOG