Civilian staff at the Faslane and Coulport naval bases have begun a series of strikes in a dispute with Babcock Marine over workers’ rights.
Unite members are taking part in a continuous overtime and on-call ban.
It coincides with “a series of staggered periods of strike action”, which the union said would have an impact on naval operations until 15 June.
Babcock previously said it was disappointed with the announcement.
Unite said the strikes would affect all areas at the bases, including the nuclear operations department.
The Faslane base on the Clyde is home to the UK’s fleet of Trident nuclear submarines.
Unite has accused Babcock of a “systematic campaign to undermine workers”, claiming it had withdrawn facilities for shop steward meetings and was “failing to meaningfully consult and negotiate with the trade union”.
The union represents a range of workers at the two bases, including cleaners, housekeepers, logistics operatives, drivers and mail staff.
It also has members in radiation monitoring and strategic weapons support roles.
Unite regional officer Stephen Deans said: “Our members have been forced into this action today. Management at Babcock Marine have engineered a complete breakdown of normal relations with workers.
“Our fear is that they want to try and undermine workers’ rights so they can cut jobs and service quality through more outsourcing.
“They want to squeeze as much money as they can out of being involved in the nation’s defence. But our members work hard supporting the Royal Navy’s operations and will not allow profit to be put before service.”
He added: “We have no doubt that this action will cause major disruption to the day-to-day services that Babcock Marine provides.
“If the company wants to resolve this dispute, it has to pledge to start acting as a reasonable employer that treats its staff as partners.”
Babcock Marine has not responded to a request for a statement.