The civil service's biggest union has announced two new trade-union recognition agreements have been reached for outsourced security staff protecting government sites.
PCS said the deals covered around 150 officers employed by G4S at Cabinet Office and Department for Science, Innovation and Technology properties.
The recognition agreements mean the union can consult and negotiate with G4S on behalf of members on important workplace issues such as pay and terms and conditions.
It also allows PCS members covered by the agreement to elect their local trade union representatives and to have an independent voice in the workplace.
PCS said the Cabinet Office and DSIT security staff were previously employed by outsourcing giant Mitie, which had refused to voluntarily recognise the union, forcing members to resort to statutory measures to secure recognition.
The "legal route" requires a minimum of 50% of employees in a workplace to be members of the union seeking recognition.
Mitie staff transferred to the G4S contract at the beginning of October last year.
Outsourced security guards who work for G4S on its Department for Work and Pensions contract are currently striking over pay and differentials.
PCS members and GMB members on the contract have staged one- and two-day strikes in recent weeks.
PCS members on the DWP contract are due to strike from 4-7 July and then 15-21 July, and from 29 July to 4 August in pursuit of a pay rise to take their hourly rates above the minimum wage.