A court in Siberia has ordered a new hearing into BP's failed bid last year to form an alliance with Rosneft, the Russian state oil group.
An attempt by minority shareholders in TNK-BP, the UK firm's Russian joint venture, to seek damages of $13bn (£8.5bn) from BP failed in November.
The court rejected claims that the planned Rosneft tie-up had hurt TNK-BP.
The new hearing comes as BP attempts to sell its 50% stake in TNK-BP after years of tensions with its partners.
BP announced on Friday that it would pursue a sale of its TNK-BP stake after receiving unsolicited approaches.
Analysts believe the 50% stake in Russia's third largest oil producer is worth about $30bn.
But the new court move by unnamed shareholders could complicate BP's attempt to extricate itself from an already difficult situation.
BP's involvement in Russia has been lucrative, but overshadowed by disputes with Alfa-Access-Renova, its partners in TNK-BP.
AAR, run by a group of Russian billionaires, has said that BP could be in breach of contract if it discloses confidential information about TNK-BP to potential buyers.
But the Reuters news agency reported BP as saying that it would "meet our obligations under the shareholder agreement and expect Alfa-Access-Renova to do the same".
AAR has denied being party to the new lawsuit. The Federal Arbitration Court in the Siberian city of Tyumen has sent the case for hearing in a lower court, but no date has been set.
There have been widespread reports that state energy holding company Rosneftegaz, which controls Rosneft, wants to buy BP's stake in TNK-BP.
BP's attempted share swap with Rosneft last year was part of an ambitious plan by the UK company to develop oil fields in the Arctic. But the landmark deal was blocked in the courts by BP's partners.