Australia has introduced its highly controversial carbon tax, after years of bitter political wrangling.
The law forces about 300 of the worst-polluting firms to pay a A$23 (£15; $24) levy for every tonne of greenhouse gases they produce.
The government says the tax is needed to meet climate-change obligations of Australia - the highest emitter per-head in the developed world.
But the opposition calls it a "toxic tax" that will cost jobs.
The opposition also argues that the tax will raise the cost of living, promising to repeal the legislation if it wins the next election, due in 2013.
Environmentalists have broadly backed the scheme, but there have been large public protests against it.
Australia's mining firms, airlines, steel makers and energy firms are among those expected to be hardest hit by the the Clean Energy Act.
Domestic fuel bills are expected to rise as companies pass on the costs to consumers.
But the Labor government of Prime Minister Julia Gillard says it is the only realistic way of meeting Australia's climate-change obligations.
It says the that low income earners will be compensated.
"People have already seen pension increases and family payment increases and this assistance to families around the country will continue," Ms Gillard told Australia's ABC.
"Businesses have got themselves ready for carbon pricing. New investments are being made."
The government also hopes that the legislation will force innovation in renewable energy supplies, and free the country from its reliance on fossil fuels.