Key Points:

Wellingtonians are being warned to expect traffic gridlock as drivers for the city's main bus service step up industrial action.

A stopwork meeting by GO Wellington bus drivers unhappy with their pay rates caused disruptions for a few hours around midday yesterday.

But drivers will now stop work tomorrow during the morning peak hour of 7.30am to 8.30am tomorrow.

Notices distributed on behalf of drivers were displayed on bus seats today and suggested adjustments to drivers' rosters in recent years had eroded their pay rates .

The notices said work hours had been reduced, which was also leading to a reduced level of service for commuters.

The city's public transport network, Metlink, to which GO Wellington is contracted, said the Tramways Union representing the drivers had recently declined a 7 per cent pay increase offer.

GO Wellington said the roster adjustments involving cuts to hours were a health and safety measure.

Acting Wellington Mayor Ian McKinnon urged bus commuters to make alternative travel plans tomorrow, or work from home if possible.

He said drivers had threatened to step up the strikes later in the week and possibly into next week.

"This has the very real potential to create absolute gridlock on Wellington roads," Mr McKinnon said.

"Tens of thousands of people travel into the central city each day by bus, and a lot of those people may have to bring their cars in over the next few days - and we're already at capacity for parking in the city."

The strikes will also affect school runs in the city, but non-GO Wellington services which operate mainly in outlying suburbs will continue as usual.

Mr McKinnon said the Wellington City Council was putting pressure on both parties to resolve the dispute.