Unions representing Auckland bus drivers were yesterday talking to lawyers about the nature of industrial action they plan to take over their contract dispute.

About 1000 NZ Bus drivers and cleaners, represented by four unions, voted yesterday to issue notice of industrial action following unsuccessful mediation to settle a pay dispute.

The dispute has been going for five months and the parties yesterday accused each other of shifting the goalposts in terms of their claims.

Gary Froggatt, spokesman for the Tramways Union, said discussions were being held with lawyers over the precise wording of the strike notice and formal notice was likely to be given to NZ Bus, owned by Infratil, today or Thursday, he said.

He would not say what the action would be other than that it would be "work to rule" - where staff work to the letter of the rulebook and no more.

The drivers' first proposed industrial action was work to rule plus the refusal to perform some extra actions. That was met by NZ Bus saying it would lock out the drivers.

NZ Bus made a new offer, but an agreement has not been reached.

The unions said drivers earned between $14.05 and $16.75 an hour, with split shifts often keeping them away from home for long hours, and that a pay offer from NZ Bus was inadequate.

NZ Bus chief executive Bruce Emson said the unions had rejected an improved offer of 4.2 per cent, 3 per cent and 3.3 per cent over three years.