Transport Minister Gerry Brownlee says the country's biggest bus company must comply with Auckland's new electronic ticketing system or face the consequences.
Repeated delays have pushed back a trial of the $98 million HOP system from April to as late as September.
Wellington-based Snapper has yet to make its technology, used by NZ Bus, compatible with the core system, which is ready to trial.
The Government is funding the majority of the HOP system, and Mr Brownlee has discussed the delays with Transport Agency officials.
He says NZ Bus and sister company Snapper will know the contractual consequences of missing the deadline at the end of November.
He says a failure to comply with the new citywide ticketing system could see NZ Bus out of the market.