"We are not wavering from our commitment to clean, renewable energy," Lekstrom said, acknowledging he was surprised by the ruling by the regulator, the British Columbia Utilities Commission.
The commission said parts of BC Hydro's plan to promote green energy production were "not in the public interest".
Lekstrom complained that the commission's refusal to let BC Hydro downgrade the operations of the natural-gas fired Burrard power plant near Vancouver will hurt efforts to cut greenhouse gas emissions.
"That's just not going to happen," he said.
Higher use of the Burrard facility could decrease the need to purchase power from other sources, including the small, independent green energy producers that the BC Hydro plan was trying to promote.
BC Hydro, Canada's third-largest electric utility, has been given a mandate by the government to make British Columbia self-sufficient in electricity by 2016.
The West Coast province has also pledged to cut greenhouse gas emissions linked to climate change by 33 percent by 2020, having enacted a carbon tax and agreed to be part of regional emissions cap and trade system that is spearheaded by the state of California.
Some critics of British Columbia's energy plans have accused it of overstating future power demand, and of allowing private firms to take control of public rivers to build small hydro facilities.
BC Hydro has not decided yet how it will respond to the commission's ruling.
The regulator did approve part some of the utility's spending plans, including continued consultation work on the proposed Site C dam, a massive hydro-electric project being considered for northeast British Columbia.