Members of the Public and Commercial Services Union have today begun their 57th day of strike action at the National Gallery, which will go on indefinitely, in protest at the transfer of 400 jobs to a private firm.

The strikes have meant that only 30 per cent of the National Gallery remains open today. A spokesman from the union said 250 people are on strike today, which PCS said will be continuous from today.

It comes a week before Gabriele Finaldi takes over from Nicholas Penny next week.

The union says it remains opposed to the “privatisation of all the gallery's visitor services and is fighting for the reinstatement of its senior representative Candy Udwin, who an interim tribunal has found was likely to have been sacked unlawfully for trade union activity in relation to the dispute”.

A picket line will be outside the gallery in Trafalgar Square between 9am and 11am each day, and Friday from 5pm to 6.30pm.

The National Gallery said in a statement that some rooms would be closed as a result of the strike action, and apologised for any inconvenience this may cause.

The statement said that the gallery has spent more than a year negotiating with the PCS union, with both parties meeting with the Advisory, Conciliation and Arbitration Service, however it says that the PCS “refused to compromise on its position”.

It added that PCS opposes the introduction of new working practices for some visitor facing and security staff which, the gallery claimed, would enable it to “operate more flexibly and deliver an enhanced service to our 6 million annual visitors”.

The National Gallery has appointed Securitas as its partner to manage some visitor-facing and security staff services. It says no members of staff will be made redundant in this process, and all affected staff will continue to be paid the London Living Wage.

The statement said: “All those staff affected will have the option to move to Securitas with the same Terms and Conditions and remain a valued part of the National Gallery family (just like their fellow staff members who are employed by DOC, Antenna and Peyton & Byrne etc).”

Mark Serwotka, PCS general secretary, said: "We had asked the new director to step in to resolve this dispute before taking over but now his first week will be greeted by a continuous strike. We remain ready to negotiate.

"We do not believe this privatisation is in any way necessary and we fear for the reputation the gallery rightly enjoys around the world as one of our country's greatest cultural assets."

By last month repeated strike action at the gallery had meant that union members had spent a quarter of the year so far on strike.