The Leonardo exhibition at the National Gallery in London faces disruption by strikes action from this week.

Warders say cuts leave works vulnerable to damage or theft. They are planning two-hour stoppages on 19 and 28 January and 2 and 4 February, with other possible dates to follow.

The strike follows the gallery's instruction to warders – now called "gallery assistants" – to each watch over two rooms rather than one.

Warders claim this allowed a man to attack two Poussin paintings in July while the warder was in the adjoining room.

A gallery spokeswoman said: "The majority of galleries … throughout the UK, across Europe and far beyond, all employ similar systems. The National Gallery will endeavour to keep the exhibition open and fulfil its obligation to people who already have tickets for that day."