Thousands of health and safety workers are holding a one-day strike on Monday in protest at a "derisory" pay offer.
Inspectors, scientists and admin staff at the Health and Safety Executive
(HSE) will walk out for 24 hours.
HSE staff, who are responsible for the regulation of safety in the workplace, will follow up the action with a work to rule.
Prospect and the Public and Commercial Services Union (PCS) said the strike would hit HSE work across the UK.
The unions said the pay offer would mean the most experienced staff would receive a rise of 1.5% this year.
Offices picketed
Richard Hardy, negotiations officer for Prospect, said the offer was "derisory" and would reduce morale among workers.
His counterpart at the PCS, Steve Farley, said the union's claim for a minimum pay rise of 2.6% was "reasonable and affordable".
But many low-paid workers would be given above-inflation rises and there was still room for compromise on detail of the proposed pay deal, the HSE said.
The strike will involve up to 3,000 employees with HSE offices across the country being picketed on Monday.
Unions said major incidents and court cases would be given dispensation from the strike.