Thousands more workers at Network Rail are to be balloted for strikes in escalating disputes over pay, jobs and conditions, the TSSA union announced.
It comes amid warnings of a "summer of discontent", with rail workers poised for the largest walkout in more than 20 years.
If members opt to strike, it could see action taken toward the end of July - and will follow widespread strikes across the sector, with separate walkouts planned this month.
