Leyton Orient Football Club has said it is confident of winning a judicial review into West Ham's proposed move into the Olympic Stadium.
A club statement said it "would not have issued proceedings if it were not confident of success" and said lawyers had advised it had a strong case.
Chairman Barry Hearn said he did not believe that the London Legacy Development Corporation (LLDC) had been fair in choosing who should be the new tenants for the venue in Stratford.
It comes after Mr Hearn expressed fears that his club could be killed off unless the LLDC agrees to let the O's share the stadium with West Ham United.
The news also follows a report in the Sun newspaper on Monday which claimed that West Ham co-chairman David Gold expected to sign an agreement over the move on Saturday March 16.
West Ham are the preferred tenants for the stadium and had been hoping to move in time for the 2015-16 season.
It is the second time that Orient has launched a judicial review over the stadium.
A previous attempt to pick a tenant collapsed and had to be started again following the legal action and complaints from both Orient and Tottenham Hotspur FC.
Mr Hearn said: "We took an interest in the stadium when we knew they were going to cover the athletics track, and our proposal for tenancy was built on a foundation of a large scale community project.
"Our plan was, and remains, to be the community offering alongside a wealthy Premier League club.
"We don't intend to interfere with West Ham's residency at the Stadium, but maintain the position that if they are going to be there, then we need to be there too."
A spokeswoman for the LLDC said: "We have been notified that Leyton Orient have made the decision to issue proceedings for judicial review.
"Whilst this is disappointing, we believe that our processes have been robust, fair and transparent and that the challenge is misconceived."
Explaining the legal basis for the judicial review, an Orient spokesman said bidders had been required to consent to sharing the stadium, which the LLDC was supposed to consider.
But he claimed this had been ignored.