LONDON (AP) — Workers at London’s National Gallery on Tuesday launched an indefinite strike in a long-running dispute over privatization, closing off large parts of one of the city’s top visitor attractions.

Members of the Public and Commercial Services union at the famed art museum have staged a series of walkouts in recent months to protest the privatization of visitor services, including security.

Picket lines were mounted Tuesday outside the gallery in Trafalgar Square. The National Gallery said many of its main exhibition rooms were closed Tuesday, along with the main entrance and access to areas such as cloakrooms.

Museum press officer Esther Saunders-Deutsch said about 30 percent of the museum was open Tuesday, and that the impact of the strike will be different from day to day.

The gallery says no jobs will be lost and that privatization would allow it to operate more flexibly and deliver better services to visitors.

The Association of Leading Visitor Attractions says the gallery attracted 6.4 million visitors last year, ranking it second behind the British Museum.