Members of the GMB, Unison and Unite unions in Carmarthenshire have each voted to take action and will not work overtime between 18 and 20 December.
One union said “more substantial” action could be taken after Christmas.
Stephen Pilliner, from Carmarthenshire council, said the authority was continuing to meet with trade unions.
Unite became the third union to vote for action on Friday and a meeting is due to take place between the unions and the council on 4 December.
The unions claim their members have some of the worst road gritting terms and conditions in Wales and want a better weekly retainer fee from the council.
They also say no-fault accidents in gritters could affect their own personal insurance claims.
According to the Local Democracy Reporting Service, Mark Evans, Unison’s Carmarthenshire branch secretary, said: “This could get very nasty, or it could get sorted out very quickly.”
Carmarthenshire’s road network stretches more than 2,000 miles (3,200km) and is one of the largest in Wales.
Speaking last week, GMB regional organiser Peter Hill, said: “Our members are angry and have given a clear signal that they are unhappy with the current arrangements.”
Carmarthenshire County Council said it would not be commenting, except to confirm the authority would be “meeting with the trade unions this week to discuss matters”.