Fire and rescue workers at a nuclear submarine base have begun an overtime ban over "major safety concerns".
Unite union said its members are taking action in a dispute over cuts to fire and rescue crew levels, and a lack of consultation.
It said that Capita management has reduced the specialist fire safety crew by eight positions at HM Naval Base Clyde, known as Faslane – home to the UK's nuclear submarines – and the Royal Naval Armaments Depot at nearby Coulport.
The union said it believes the cuts impair the abilities of the onsite fire crews to do their jobs properly, particularly in relation to incidents that would involve wearing breathing apparatus.
Unite industrial officer Debbie Hutchings said: "Unite's fire and rescue workers at Capita will start an overtime ban from Thursday 16 September over our major safety concerns at the Coulport and Faslane naval bases.
"We have been in dialogue with Capita since their decision to press ahead with cutting the fire response services at the bases, but more concerns have been raised throughout this process."
Watch: Faslane in 2015 – inside Britain's nuclear submarine base.
She went on: "There is a lack of clarity, cohesion and co-ordination about what would exactly happen in several major incident scenarios. We simply haven't received any credible answers to our questions.
"It's deeply worrying that in all the years the bases have been in operation, there hasn't been a practical exercise for maximum credible incident scenarios with all the relevant agency involvement.
"These are routine exercises which are regularly done on other safety-critical sites but they are not happening at the naval bases," she added.
Unite said members at Capita supported taking action short of a strike by 100%, while 78% supported taking strike action in a ballot turnout of 91.1%.
The company provides fire response services for the Ministry of Defence (MOD).
A Capita spokesman said: "We are disappointed by Unite's decision to proceed with industrial action regarding MOD-approved changes that have been made to resourcing levels at Faslane and Coulport.
Watch: COVID – nuclear mission kept afloat as Royal Marines install Faslane test site.
"We have a range of contingency options agreed with Defence Fire and Rescue and the Royal Navy's Clyde leadership team which will ensure the delivery of fire service operations is maintained.
"Our recommendations to increase or decrease resourcing levels at any MoD site have to be endorsed by Defence Fire and Rescue's Chief Fire Officer, and ultimately approved by the site's leadership team.
"Any such decision would follow on from a thorough review of fire risks.
In this case, our proposed changes were also validated through the conduct of four confirmatory exercises and a lengthy process of scrutiny by the base leadership team.
"Capita is working with Defence Fire and Rescue to modernise the MOD's fire and rescue capability. Our £85m investment in new firefighting vehicles, digital technology, and enhanced training facilities is improving firefighting capabilities and reducing risk to our firefighters, MoD personnel and critical military assets," the spokesman added.
The company said that HM Naval Base Clyde is due to receive four new firefighting vehicles by the end of the year and is in the final stages of agreeing the location of onsite Breathing Apparatus training facilities at Coulport, to improve firefighter safety and minimise the need for firefighters to travel for training.
A Navy spokesman said: "Safety at HMNB Clyde will not be compromised by the proposed industrial action and Capita will provide contingency arrangements to ensure that on-site fire and rescue cover is maintained."