For its National Broadband Network (NBN), the Coalition plans to run fibre optic cable to nodes and use the existing copper wire network to link the rest of the way to buildings to save money.
But Strata Community Australia (SCA) said this disadvantages apartment building residents, because the aging copper wire infrastructure within such premises won't be able to cope.
"For apartments, they are dreaming if they think they are going to get 25 megabits per second [Mbps]," SCA chief Mark Lever told AAP on Wednesday.
"Most residents in Bondi will have worse internet connections than in Boggabilla [in far north inland NSW]."
Under Labor, the network builder NBN Co will run fibre all the way to residential buildings, which will then run through the existing copper wire conduits to individual apartments.
But under the plan announced by Opposition Leader Tony Abbott and his communications spokesman Malcolm Turnbull, that would not happen.
"Apartment residents will not get high-speed broadband under this plan," Lever said.
The opposition has said that residents can pay for fibre to run all the way to premises if they want.
However, this won't help individual flat residents wanting to pay the extra, because there is no avenue to act without the agreement of owner corporations, which control building infrastructure.
Lever also fears that most wouldn't want to spend the money.
"You require 75 percent of owners to agree, and individual owners can't go out and pay," he said.
"Certainly, for apartment dwellers, this is a policy that doesn't guarantee deliverable high-speed broadband."
Abbott has promised to deliver fast broadband to Australians earlier and cheaper than under Labor's NBN.
The plan has been dubbed a "lemon" by some experts, because it will only provide minimum speeds of 25Mbps, compared to Labor's 100Mbps.