A strike by workers at the Passport Office is to be escalated next month.
The Public and Commercial Services Union (PCS) said its members in all Passport Offices will walk out for four days at the beginning of May.
Union members have been taking industrial action since the start of the month, but it has been limited to some staff in some offices.
Almost 2,000 PCS members working as passport examiners in Belfast, Durham, Glasgow, Liverpool, London, Newport, Peterborough and Southport have been on strike since April 3 in the union’s long-running dispute over pay, pensions, redundancy terms and jobs.
PCS general secretary Mark Serwotka said: “At every stage of this dispute we have warned we will escalate action if our demands are not met.”
He said the Government had “insulted” civil servants last week by announcing they will receive a pay rise this year of between 4.5% and 5%.
Mr Serwotka added: “Our members are not prepared to be treated this way, which is why we are escalating our action.
“Ministers can stop these strikes and ease the passport backlog tomorrow by making a reasonable offer to our members.”
More than 130,000 PCS members will stage a nationwide strike on April 28.