"Auckland Transport will not be commenting further on this matter."
The bus company's chief northern operating officer Shane McMahon said it had a set amount of weekend work it was contracted to perform, and wanted to share across all drivers to be fair to all.
That will end a seniority exemption now extended to those with longer service.
"We believe sharing that weekend work across all employees is fairer and means that some of the younger drivers with families are not required to work an excessive number of weekends," Mr McMahon said.
"We appreciate there will be vocal resistance from a few drivers who are seeking to maintain their position, but it is about doing what is right for the majority of our people."
But Tramways Union president Gary Froggatt said the changes would affect about 600 drivers at all levels of seniority from five depots, requiring them to work clusters of up to five weekends in a row rather than one in three as many do now.
"It means they may not be able to go to church - a lot of drivers have religious affiliations," he told the Herald.
He said the company also intended increasing unpaid time in the middle of daily split shifts to four hours, from three hours now.
First Union organiser Rudd Hughes said the company had consistently ignored feedback from drivers, who needed rosters "which will keep passengers safe and provide a decent work-life balance."
He said the two unions had provided alternative roster proposals, but the company had rejected those.
Mr McMahon said the company was willing to consider the cases of drivers with exceptional circumstances, and had made an offer to the unions accordingly.
He said NZ Bus was committed to "transforming" transport in Auckland, as attested by an improvement in punctuality to 94 per cent of buses leaving their origin stops no more than five minutes late last month, compared with just 83 per cent two years ago.
Mr Froggatt said tomorrow's protest demonstration from 12 noon to 12.30pm will be by drivers either on lunch breaks, or otherwise off-duty, and is not aimed at disrupting passenger services.