The dispute involves dozens of Inverness-based staff who maintain and keep safe key routes across central Scotland and the Highlands, including tsupporting the A9 Dualling programme between Perth and Inverness.

Workers have thrown out a pay offer from Bear which would have lifted the lowest rate from £12 to £12.75 an hour and increase the top grade from £13.25 to £14.25.

Construction union Unite said the offer fell short of what workers received at rival contractors that pay up to £16 an hour for similar work.

Unite industrial officer Marc Jackson said:“The workers are essential to one of the nation’s key transport infrastructure upgrades, yet they are being treated poorly by Bear Scotland and paid well below workers at other maintenance companies.

“Bear needs to get back round the negotiating table with an improved pay offer. If they don’t heed this advice, then industrial action during the bad weather when these workers are needed the most will be inevitable”