Rail signallers have announced a new phase of strike action in a long-running dispute over shifts.
Signallers in the Stirling area will halt work this weekend as workers continue to demand a move from eight to 12-hour days.
The RMT union has accused Network Rail of the "flagrant violation" of rostering agreements.
The rail operator said the shift changes would incur tens of thousands of pounds in extra operating costs each year.
RMT said in a statement: "For many months now RMT has attempted to negotiate an agreement with local management over 12-hour rosters within the framework agreement on rostering agreed between management and the unions.
"Regretfully, despite considerable efforts by RMT's local reps, management refuse to budge on the call for the 12-hour rosters which staff in the Stirling area have requested in line with existing rostering policy and which the union knows will deliver a safe and efficient service."
Workers at Stirling Middle, Stirling North and Dunblane will strike for 24 hours from just before midnight on Friday in what the RMT describes as one of the longest-running disputes anywhere in Britain.
It is understood that there will be sufficient staff cover, however, and passengers will not be disrupted.
A Network Rail spokesman said: "We remain committed to finding a solution to the current dispute and will continue to engage in talks with the RMT, and through (dispute settlement body) Acas. We are confident we can run a comprehensive service for passengers should industrial action take place and that the travelling public will not be inconvenienced by the RMT.
"Meeting the union's demand that signallers begin to work fewer days each week would mean operating a less efficient and more expensive railway."