The federal opposition's decision to delay the final vote on legislation to introduce an emissions trading scheme (ETS) could affect investors' portfolios, as the increased uncertainty could have a negative effect on heavy-polluting businesses.

"Investors face increased uncertainty over the future of high-polluting assets due to delays in an agreement on climate change legislation," Fitch associate director Sajal Kishore said.

"Three Victorian brown coal-fired generators have $1.7 billion of debt facilities maturing over the next 18 months, and Fitch expects that further uncertainty may affect refinancing," Kishore said.

Australia's two main political opposition parties said on Tuesday that they want the government to delay the vote until after the global climate change talks in Copenhagen in December.

The increased uncertainty could depress stock prices of heavy polluters, such as mining and energy generating companies.

Investors are generally seeking early resolution of these issues, the rating agency said, although delays in the implementation of the scheme may benefit emissions-intensive businesses in the short term if a lower cost outcome can be achieved.

Delaying the carbon trading scheme could also result in businesses missing out on billions of dollars in assistance to heavy-polluting, trade-exposed industries, parliamentary secretary on climate change Greg Combet said yesterday.

Delaying the vote on the scheme until next year may force the government back to the drawing board.

"If we have to go back to the drawing board, everyone involved will have to run the gauntlet of the political process - something we know cannot guarantee certainty," he said.