PM&C told its workforce that managers already very busy with the tricky task of putting together a pay deal would have to drop everything in the event of industrial action to administer the strike.

Meanwhile over at Immigration and Customs, bosses say their 13500 officials, who have been waiting 10 months for a pay offer, would be jumping the gun by walking off the job.

Bosses at the soon to be merged departments say talks, on a new enterprise agreement to replace the one that expired in June 2014, are still at an "early stage".

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Union negotiators at PM&C fired a shot across the department's bows in late March, saying they were gauging support for industrial action that would be on the cards if a "fair and reasonable" pay offer was not received by May 1.