Union leaders claimed to have "rock solid" support for a 24-hour walkout by rail workers.
Some 560 guards and drivers are said to be on strike in Scotland, in a dispute over the absence of conductors on a new service.
It is the third 24-hour strike this year over the plans for drivers to operate the doors on a line from Glasgow to Edinburgh via Airdrie and Bathgate, with a ticket examiner as the second person on board.