As rail workers' industrial action continues, buses will be running along all of Auckland's train routes on Sunday to cover any reliability problems.

Unionised staff of rail operator Auckland One Rail (AOR) have been taking action since last weekend because negotiations towards a new collective agreement are at an impasse. Rail workers are refusing to work overtime or work changes to rostered hours, and Auckland Transport said that means the operator was unable to confirm which trains would actually be running.

And workers from Construcciones y Auxiliar de Ferrocarriles (CAF) - which maintains the trains - are only doing scheduled checks on trains, and not any other repairs or breakdown-related work, or overtime.

The Eastern, Southern and Western lines would have a rail bus every 20 minutes during the day and every half-hour in the evening. Rail buses on the Onehunga line have been scheduled for every half-hour all day.

Normally these train services would run as frequently as every 10 minutes at peak times.

The Puhinui Express bus would run every 30 minutes between Britomart and Puhinui via Newmarket.

"We understand that both AOR and CAF have committed to mediation with the RMTU (Rail and Maritime Transport Union) and we're hopeful that discussions will bring about a quick resolution to these issues," AT rail franchise manager Craig Inger said in a statement.

"Our customers have shown a great deal of patience and it is increasingly disappointing that ongoing industrial action continues to disrupt the rail services which they rely on."

Passengers can check its app for live updates on which services were operating, and timetables for the rail buses were available on its website.

AT's site warned of "ongoing impact" to train scheduling.

"Due to the industrial action there may be cancellations to some services. Which services are cancelled may vary each day depending on staff availability."

Last week, the RMTU said the previous collective agreement expired eight months ago and negotiations had stalled with "a couple of major issues that we haven't been able to get past".

This story was originally posted by RNZ News