TAXPAYERS will fork out billions to deliver fast broadband to rural Australia before cities, the coalition claims.

Labor has promised to roll out broadband to the country first as part of the deal with rural independents Tony Windsor and Rob Oakeshott.

But The Australian reports shadow finance spokesman Andrew Robb said the promise would undermine the project’s business case.

"The NBN business plan was to minimise the cost of the rollout and keep the maximum public exposure to $26bn by first attaining a critical mass in the cities that would allow them to generate revenues to assist the regional rollout, but now that whole thinking has been turned on its head," Mr Robb said.

Communications Minister Stephen Conroy yesterday defended the government's move to prioritise rural areas, saying the move would not cost taxpayers any extra money.

However, he acknowledged that NBN's timetable for completion would need to be adjusted.

"We'll be talking to the team at the National Broadband Network Company over the next few days about how we can redesign the rollout timetable, so this is a question of a timetable about where they'll start rather than any increase in cost," Senator Conroy told the ABC.