Auckland Mayor Len Brown wants answers from KiwiRail after two breakdowns in two days caused long delays for many of the city's rail commuters.
Trains were halted for about 40 minutes during peak hour on Wednesday night after a fault in the Auckland signalling system, impacting on thousands.
The next morning, commuters on the lines going through south Auckland and east Auckland were delayed after the cutting of a telecommunication cable overnight stopped all train services between Pukekohe and Puhinui.
Taxi shuttles were in place between Pukekohe and Papakura but couldn't mitigate all the delays.
Mr Brown has made improving public transport one of the key planks of his mayoralty and he wants an explanation from KiwiRail.
"We need assurances from KiwiRail that they are doing everything they can to ensure there is no repeat of this disruption," he said.
"As Aucklanders look forward to electrification and the arrival of our new train fleet, they need confidence that train services are reliable and on time."
KiwiRail chief executive Jim Quinn says both incidents are being investigated.
"We understand how much frustration this disruption will have caused people who rely on the trains, and we sincerely apologise for that."
He said work was under way to repair the cable damaged near Papakura, while technical teams were trying to understand Wednesday's problem.
"It was a local Auckland fault, and with complex equipment such as that it can take some time to pinpoint the cause."
Mr Brown said he appreciated Mr Quinn's apology and was confident KiwiRail would work hard to prevent a repeat.