The Library’s 281 staff have not received a consolidated pay rise since 2009. Prospect, representing the specialist staff, said this amounted to a 20% pay cut in real terms, and 14 staff were now below the Living Wage – the minimum which the Welsh Government says public sector workers should earn.

Prospect negotiator Jane Lancastle said the union was concerned about the impact on individual staff, who were struggling to make ends meet, and about the future of the library itself. “This is a national institution which cares for the heritage of Wales. But it is losing skilled and experienced staff, and failing to attract new staff due to uncompetitive wages.”

“Librarians and archivists aren't radicals. Something is really wrong when they go on strike. Our members care passionately about the work they do and the service they provide. We want to secure the future of the library, but we can't do this if management won't listen to us.”

In Prospect’s ballot, 92.8% voted in favour of industrial action. Two other unions – FDA and PCS – balloted separately, and members of all three unions will be taking action on 10 September.

Picket lines will be at the Library entrances from 8am on the day. At 12 noon, staff will march from NLW to Sgwar Glyndwr in Aberystwyth for a rally from 12.30-1pm - speakers to be confirmed.