The heads of the 12 leading firms say climate change is a huge challenge that needs serious investment by business.
But they say they cannot invest because they are not sure what future government policies on climate will be.
The letter is signed off by the heads of BP, Shell, HSBC Bank, BAA, John Lewis, Scottish Power and more.
Between them the firms employ more than 750,000 people and have a turnover of £452bn (approx US$765bn).
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