HONOLULU -- The state Supreme Court heard legal arguments that could scuttle the Hawaii Superferry again.

The only reason the Hawaii Superferry is operating without an environmental assessment is because the Legislature gave it a break from the law. Environmental lawyers said that is both unfair and unconstitutional.

Hawaii Supreme Court justices on Thursday seemed very interested in that argument.

"The Legislature specifically chose to act in this situation and speak on behalf of the entire state it is perfectly within their authority to do so," 1st Deputy Attorney General Lisa Ginoza said.

Lawmakers wrote the law for so-called "high-speed large-capacity ferries" after the courts ruled Superferry needed an environmental assessment that could delay its start up, but the state Constitution does not allow laws that give an advantage to a single entity.

"The act is actually conceived cut and tailored for Hawaii Superferry alone," said Isaac Hall, attorney for environmental groups.

The justices focused on that issue.

"Is there any entity that would fit that description except for Superferry?" Justice Simeon Acoba asked the state's attorney.

"There are specific provisions contemplating other ferries coming into this state," Ginoza said.

"Did they sign this agreement, those other ferries?" Acoba said.

"No," Ginoza said.

If the court agrees the special Superferry law is unconstitutional it would mean an immediate shutdown and months of delay.

There is an environmental impact statement now being prepared for the Superferry, which would be finished in the spring, but now that the court has thrown out the special legislation, that process will have to begin all over again, environmental lawyers said.

"The company will have to determine whether it can stick around to comply with the old law," Ginoza said.

Environmentalists say every day at sea Superferry poses a risk.

"There's harm that is actually happening," Hall said.

If the state and Superferry lose the case, they could go back to the Legislature and try again.