Manitoba Hydro is defending it multimillion-dollar expansion plan as critics of the Bipole III transmission project call on regulators to slow it down.

The Bipole III Coalition has asked the Public Utilities Board to review the expansion plan, claiming that the public power utility's forecast for future electricity demand is "vastly overstated" and will cost taxpayers more money in the long run.

"I believe it to be misleading. It's unrealistic to project spending $34 billion on a plan premised on a low growth that just is inconsistent with what recent trends have been in Manitoba," Garland Laliberte, the coalition's vice-president, told CBC News.

Laliberte, a former dean of engineering at the University of Manitoba, said Hydro's own forecasts do not take into account the flattening of the load growth in Manitoba over the past eight years.

"I am concerned as a Manitoban because if we build more capacity than we have the ability to pay for, rates for Manitobans will go sky-high," he said.

But Manitoba Hydro spokesperson Scott Powell disagreed with the coalition's claim that the expansion plan will cost taxpayers more.

"The plan is going to be reviewed independently by the Public Utilities Board. They have independent experts coming in to review our plan," Powell said.

"We're confident that once they take a look at our plan they're going to agree that it is the best way to meet the electrical needs of Manitoba going forward."

Powell said Hydro is proposing small regular rate increases to cover the expansion, but he insisted that Manitobans will still enjoy low rates in the long term.

The planned expansion accounts for $20.3 billion of its $34-billion capital plan, he added.