The mining industry spent $2.5 million pushing the case for "clean coal" in the run-up to last year's election, electoral funding records have revealed.

As coal's future in Australia's energy mix continues to dominate political debate in Canberra, returns lodged by so-called "third party campaigners" to the Australian Electoral Commission show a little-known group called ACA Low Emissions Technologies Limited was one of the top five spenders of 52 third parties.

The company, which had not previously lodged a return, was only outspent by GetUp, the Australian Education Union, the ACTU and the Business Council of Australia but massively outspent renewable energy advocates the Solar Council, which spent $36,000, and Greenpeace, which spent $53,000.

ACA Low Emissions Technologies takes its name from the former Australian Coal Association which merged with the Minerals Council of Australia in 2013.