BHP is facing the prospect of a seriously a beefed-up class action over its Samarco dam collapse after a court ruled two class actions against the miner should be combined.

Maurice Blackburn last week partly won its appeal against a Federal Court decision last year that threw out its class action claim against BHP in favour of a separate class action brought by boutique law firm Phi Finney McDonald (PFM).

The Full Court of the Federal Court found that Maurice Blackburn and PFM should find a way to work together.

The decision means BHP will now face a much strong class action claim with Maurice Blackburn and PFM pooling the thousands of investors who have signed up into a single claim.

The decision is also expected to increase the firepower in the claim with the well-resourced and experienced law firm Maurice Blackburn adding some serious muscle to the PFM case.

BHP is vigorously defending the claims.

The Full Court ordered both firms to have discussions by June 10 about how they might combine the proceedings. The matter will return to court if the two firms are not able to agree to a combination of the class actions. It is unclear how the case will proceed if the two firms are unable to reach an agreement.

A separate, third claim against BHP by law firm Johnson Winter & Slattery on behalf of BHP investor Los Angeles County Employees Retirement Association was not part of the appeal. That case was thrown out by the Federal Court.

About 30,000 shareholders have signed up to the PFM and Maurice Blackburn claims, including nearly 300 institutional investors.

The class actions relate to the failure of the Fundao tailings dam in Brazil in 2015 which was operated by the Samarco joint-venture between BHP and Brazilian miner Vale SA.

The mudflow from the dam killed 19 people and caused an environmental disaster and led to a slew of legal cases against the venture and its partners. This includes criminal prosecution for homicide charges that have been laid against current and former BHP executives. BHP and Vale are also facing class actions in the US from shareholders and noteholders over the dam collapse.

Both the Maurice Blackburn and the PFM claims allege BHP shareholders suffered losses due to poor disclosures about the safety and environmental risks of the project by the miner.

Maurice Blackburn’s class action is unfunded and is being run on a no-win, no-fee basis. PFM’s case is funded by a US group which will get up to 18 per cent of any settlement or judgment payment, though that arrangement left the final proportion in the hands of the judge.

Maurice Blackburn national head of class actions Andrew Watson welcomed the Full Court decision.

“If the case is successful it will provide investors with greater returns than the alternatives,” Mr Watson said.

“It’s obvious from the structure of the court’s orders that they are hopeful that we will be able to reach some sort agreement with Phi Finney McDonald about a consolidated proceeding.”