Extras have complained they are being hired below agreed industry minimum rates to appear in a movie starring Keira Knightley.
They are being paid £100 for a 12-hour day to work on the big-screen adaptation of Anna Karenina – with the British actress in the title role.
The rate is below the minimum fee agreed under the terms of a Film Artistes Association (FAA) agreement between Bectu, the entertainment union, and Pact, the Producers Alliance for Cinema and Television.
The agreement requires any extra working on a Pact film to be paid £83.72 for a nine-hour day, with overtime paid at £7.84 an hour.
Under the agreement, Karenina extras should be paid a minimum of £130.76 for a 12-hour day, with expenses for travel, the union claims.
Paul Kirby, chairman of the FAA, told The Stage that he was "very disappointed" with the rate offered by Pact member Working Title, behind hits like Four Weddings and a Funeral and Atonement.
Mr Kirby said: "On this film the extras' fees – even at the correct rate – would not be more than 1 per cent of the entire budget."
The minimum Equity rate for a nine-hour day is £65, with overtime paid after that at time-and-a-half.
Working Title was unavailable for comment.