HONOLULU -- Officials with the Hawaii Superferry on Monday evening announced in a written statement that the company will voluntarily halt sailing between Oahu and Maui following a ruling by the state supreme court.

Justices at the Hawaii Supreme Court on Monday morning issued a ruling that says legislation passed by state lawmakers to allow the Hawaii Superferry to operate while conducting an environmental impact study was unconstitutional.

The Legislature passed Act 2, allowing the ocean transit company to continue to sail while an EIS is done, after the high court ruled in September 2007 the company must conduct a study.

In December 2007, Gov. Linda Lingle signed Act 2.

The Sierra Club then challenged the constitutionality of Act 2.

The justices ruled that "Act 2 constitutes unconstitutional special legislation."

"I think it is a great victory for Hawaii's environment," said Isaac Hall, the attorney for Maui opponents and the Sierra Club. "It's something the Sierra Club has said consistently is that this was special legislation that was targeted for just one business and one entity and that's unconstitutional."

Lingle said she believes the Legislature had the clear authority to pass that law.

"We know from the beginning we were correct and accurate, did the right thing, and we've been able to provide a great service for the people of Maui and Oahu," Lingle said.

"We believe very strongly that the Legislature acted properly," Lingle said in response to the Supreme Court's ruling.

The Hawaii Superferry issued a statement late on Monday afternoon:

"Obviously we are hugely disappointed with the Supreme Court¹s decision that Act 2 is unconstitutional. We have operated on a regular, reliable and responsible basis for the past 11 months. During this time over 250,000 people have booked travel on Alakai and it has provided new economic opportunities for Hawaii¹s businesses.

While the appeal is not yet final because a judgment on appeal has not been entered, we want to proceed prudently and have decided to cease operations for the present.

Our first priority is to take care of our customers, both those who have recently traveled and need to return to either Oahu or Maui and those who have future bookings. We will make one additional round trip to get vehicles back to their homes this Thursday."

The Supreme Court also ruled that the Hawaii Superferry must pay for legal fees accrued by the Sierra Club.

While the justices did not rule that the ferry must halt operations, Hall said his group will send letters to Superferry asking the company to stop sailing until the environmental study is done. If the company did not voluntarily comply with completing the study, Hall said his group will go back to Circuit Court to try and stop the ferry.

"I think it would be devastating for the Superferry to stop operating," Lingle said.

The governor said she will consider appealing the ruling, but she has to discuss the issue with lawmakers and the attorney general.

"We're going to make sure the taxpayers are protected and that the Superferry keeps operating," Lingle said.