The legal battle over the WA Government's controversial Roe 8 highway extension continues, with the Save Beeliar Wetlands group taking its case to Australia's highest court.

The group will today file special leave to challenge last month's decision that saw a ruling against the State Government overturned by the Court of Appeal.

Roe 8 is a key part of the $1.6-billion Perth Freight Link project, which seeks to build a byway for heavy haulage from Perth's eastern industrial suburbs to Fremantle Port.

In December, Supreme Court Chief Justice Wayne Martin ruled that the Environmental Protection Authority's (EPA) assessment of the project and recommendation to Environment Minister Albert Jacob was invalid, along with his subsequent approval.

The Government appealed that decision and won, prompting the environment group to take the legal battle another step further.

Save Beeliar Wetlands convenor Kate Kelly said the group had a civic responsibility to continue to fight the highway extension.

"Roe 8 is the first stage of the Perth Freight Link which can only be described as a total mess," Ms Kelly said in a statement.

"By any standard, this project is culturally, economically and environmentally destructive and a suboptimal choice for our state's ongoing health."

Ms Kelly said the group had launched a crowd funding campaign to help it meet its legal costs.

She is expected to address the media outside the Commonwealth Law Courts on Friday.