Opposition Leader Tony Abbott has warned businesses not to invest in carbon offsets, because a future Coalition government will rescind the carbon tax.

The House of Representatives this week passed the government's clean energy legislation, which will put a $23/tonne fixed price on carbon emissions from July 1, 2012, and bring in an emissions trading scheme from 2015.

Under the scheme, which is set to pass the Senate next month, a large portion of emissions reduction will come from Australian businesses buying carbon offsets from overseas.

Mr Abbott told a tax forum in Sydney today that scrapping the scheme would be a Coalition government's first order of business.

"An incoming Coalition government's first instructions to the public service would be to prepare legislation to rescind the tax," Mr Abbott said.