Staff at the National Museums of Scotland have begun a week-long strike over a wage dispute.

The industrial action will disrupt the program at Edinburgh’s National Museum of Scotland and the National War Museum, and coincides with the Edinburgh Festival, one of the city’s busiest period.

The Public and Commercial Services union (PCS) announced that 120 members have joined the walkout after negotiations with National Museums Scotland (NMS) broke down.

The trade union explained that staff were unhappy about the introduction by NMS of a two-tier weekend pay rate system. Under the new system staff employed before 2011 get a weekend allowance, whereas staff employed after 2011 do not.

According to union officials, staff working without the weekend allowance earn between £2,000 to £3,000 less per year.

“This has been an 18-month long dispute now and essentially it’s about fair pay,” PCS Scotland’s industrial officer Alan Brown told the BBC. 

“If someone was employed by the National Museum of Scotland in December 2010 and worked weekends then they earn between £2,000 and £3,000 more than a colleague working beside them if they joined in January 2011,” he added.

A spokeswoman for National Museums Scotland confirmed that both the National Museum of Scotland and the National War Museum would be partially closed.

The National Museum of Scotland was the most popular institution in the UK outside of London last year, attracting 1.6 million visitors.

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