Australia's Western Force have been dropped from next season's Super Rugby, the Australian Rugby Union said on Friday, prompting an immediate threat of legal action by the club.

The ARU said it decided to discontinue the Force's Super Rugby licence after weeks of consultation with rugby bodies and stakeholders, including government and commercial partners.

It follows a decision to trim the southern hemisphere competition back to 15 teams after its growth to 18, including sides in Japan and Argentina, proved unwieldy and unpopular.

Perth-based Western Force and the Melbourne Rebels, traditionally the weakest of the Australian teams, had both been warned they could face the axe after the ARU promised to move from five teams to four.

"The ARU Board has today made the decision to discontinue the Western Force as the Super Rugby competition reverts to 15 teams for the 2018 season," ARU chairman Cameron Clyne said in a statement.

"This has been a complex process to reduce Australia's Super Rugby representation to four teams as agreed by SANZAAR following its review of the competition," he said, referring to the league's governing body.

However, this is not necessarily the end of the long-running saga, with Western Force's parent body Rugby WA likely to take the case to the Supreme Court if it wins the right to appeal.

"Rugby WA remains committed to pursuing every possible means to ensure the Western Force remains a Super Rugby team in Perth," Rugby WA said in a statement after the ARU decision.

"Rugby WA is considering all options including bringing urgent proceedings in the Supreme Court of NSW, and legal action relating to the circumstances which led it to enter into the Alliance Agreement with the ARU."

Billionaire mining magnate Andrew Forrest has also backed a campaign to save the Force from a cull, telling the ARU his support for rugby is contingent upon the franchise remaining in a national competition.

"Whilst the board of Rugby WA is extremely disappointed with the ARU's stated position, with the support of the rugby community and numerous WA business identities including Andrew Forrest we will continue the fight to retain the Force in Western Australia," Rugby WA said.

Clyne and ARU chief executive Bill Pulver were due to hold a press conference to discuss their decision in Sydney later Friday.

Two South African sides, the Central Cheetahs and the Southern Kings, have already been cut from future Super Rugby competitions under a South African rugby commitment to drop their representation to four teams.

Source: AFP