TNK-BP may have to hold another general meeting to elect a new board
The Russian co-owners of TNK-BP have threatened legal action following the election of a new board of directors.
The oil company is a 50-50 joint venture between Britain's BP and AAR, which represents a group of four Russian billionaires.
Four Russian nominees asked to pull out of the nine-member TNK-BP board on Wednesday, but the deadline had already passed and they were elected.
AAR said the board was illegal because the four had withdrawn from it.
Russian law requires the board to have at least nine members.
AAR complained that five of the directors were supporters of BP.
BP and AAR have been locked in an increasingly public spat over the running of their joint venture, with the Russians accusing TNK-BP's chief executive, Robert Dudley, of running it only in the interests of BP.
The final straw that led to the dispute becoming public was a row about a proposed new development in the Kurdish zone of northern Iraq, according to the Times newspaper.
No Western oil companies have yet signed agreements with the regional government of Iraqi Kurdistan, because of concerns that the government in Baghdad could annul contracts.