The planned change would mean the route to Brockville ran to the Exchange, up Rattray St and City Rd, through Belleknowes, before heading down Stone St to Brockville.
The residents, who have begun a petition to oppose the move, say that would add time to the bus trip that used to travel to the city via Stuart St.
It will also make it difficult for people in a suburb with no major supermarket to visit shops in Roslyn, and would end a direct route to Moana Pool.
The changes are suggested in the Otago Regional Council's draft regional public transport plan, a document that contains sweeping changes expected to lead to faster and more direct routes away from smaller residential streets.
The draft plan includes a central-city hub for a system set to cost more than $100 million in the next decade.
The plan is going through a consultation period, with submissions closing on Friday.
Brockville Community Support Trust secretary Marie Laufiso and board member Jasmine Hunter said they were alerted to the change by Bus Go Dunedin, a bus lobby group.
Group chairman Peter Dowden said Brockville was served by a bus every 40 minutes.
The regional council planned to cut the service to every 60 minutes in off-peak times.
''Of all the bus service plans described in the Otago Regional Council's draft regional public transport plan, Brockville would receive the greatest reductions in service,'' Mr Dowden said.
ORC support services manager Gerard Collings said the present system's frequency varied from between 15 and 40 minutes throughout the day.
''What we're proposing in the interim is a 30-minute peak, and 50-minute off-peak.
''Long term, it will be 30-minute [frequency] from 7am to 7pm, and 60 minutes after that.''
On the change in route, Mr Collings said the present route was already diverted though Bradford.
But Ms Laufiso said that was not always the case.
Ms Hunter said while collecting signatures she had met people who used the bus to get to the Roslyn supermarket, or visit the Yvette Williams Retirement Village in Highgate.
Children would get the bus directly from Brockville to Moana Pool.
All those trips would be much harder.
The residents' petition opposed both the frequency reductions and the route change.
It called on the ORC to improve the service instead of cutting it, and asked for a rapid, direct route to the city centre along main roads.
The petition also called for a service every 15 minutes, as the draft plan had proposed for Halfway Bush.
Ms Laufiso said the petition and a submission on the plan would be handed to the council by Friday.
Mr Collings said residents' concerns on the issue would be considered, noting that: ''It is just a draft plan.''
