More than 110 First Dorset drivers, based in Weymouth and Bridport, will walk out from 04:00 BST on Monday until the early hours of 25 June.
Union unite said its members were angry at a 2.3% pay offer from First Group, while its drivers for the firm in Bristol had been given a 13% increase.
The operator has described the action as "totally unnecessary".
Unite said Weymouth and Bridport drivers earn Â£8.80 an hour while drivers in Yeovil are on Â£9.50 an hour, and those at rival firms in Bournemouth and Poole earn nearly Â£2 an hour more.
It said "insufficient progress" had been made during talks on Thursday, stressing negotiations began back in December.
"We appreciate that the dispute will inconvenience the travelling public, but the ball is firmly in the management's court as they have steadfastly refused to rectify the pay inequality of our members over many years, compared with other First Group drivers across the West Country," said the union.
First Dorset said it was "disappointed" strike action was going ahead "despite our best efforts to try to reach a formal settlement".
A spokeswoman said: "First Dorset sets the pay rate irrespective of what the other companies are offering their staff.
"They are not set nationally - they are agreed locally between the local operating company and local union representatives."
The operator said contingency plans were being put in place and it has published an emergency timetable ahead of the strike action.
A five-day strike by bus drivers in Dorset will go ahead after last ditch pay dispute talks broke down.