An environmental group has written to 145 of Australia's biggest companies, warning of risks of multi-million dollar charges and potential lawsuits if they fail to control greenhouse gas emissions. Major resources companies such as BHP Billiton and Rio Tinto received the letter from Climate Action Network Australia (CANA), which tells company directors they could be responsible for costs resulting from environmental harm attributed to their companies. The letter was also sent to companies that invest in "major emitters", such as major banks, and companies which sell and burn fuel, including Caltex and Qantas.