Members of the PCS civil service workers’ union at the National Gallery in central London struck on Wednesday of last week.
Some 140 non-shift warders struck over attempts to impose changes to their terms and conditions which would see their holiday entitlement cut.
Workers had also walked out on 11 July.
Staff are angry about gallery management’s plans to impose changes to terms and conditions that include the withdrawal of the extra three days holiday staff receive in recognition for working Christmas Day, Boxing Day and New Year’s Day when the holiday falls on a weekend.
Management are replacing this entitlement with two days unpaid special leave and a one-off payment of £100.
The warders who protect one of the finest collections of paintings in the world are among the lowest paid in the culture sector, earning as little as £13,562 a year with many earning a basic rate of pay of just over £6 an hour.