Hearn believes the London Legacy Development Corporation has broken its own rules in not allowing the League One club to be 'teamed' with the Hammers in the bidding process.
Hearn, who wants his own club and the Hammers to become joint tenants of the £429million stadium, has repeated his claim that the Os will have no future if the Hammers move in.
Hearn told his club's official website: "I was concerned that this was a done deal for West Ham before the bidding began, but the fact that both clubs had to commit to teaming made me believe that we were getting involved in a fair process.
"However, the LLDC have not stuck by their own rules and have left Orient with no option but to challenge their decision in the Courts.
"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.
"As I have said many times before, if West Ham move to the stadium and we are left a mile up the road, Leyton Orient will not survive."
- Sports & Recreation