Ed Miliband is to tell small businesses he will protect them from “unacceptable treatment” by energy firms, the BBC has reported.
In a speech, he will pledge to set up a regulator to stop firms being “rolled” on to higher tariffs and forced to pay “crippling” back-dated bills.
He will say a Labour government would ensure small firms were given the same legal protections as householders.
Chancellor George Osborne’s Budget outlined a freeze on the “carbon floor” - a fossil fuels tax - for firms.
The move will save medium-sized manufacturers £50,000 a year by 2018, the government said.
Some of the biggest energy firms raised their tariffs at the end of last year, and energy prices have become a keenly contested political issue in recent months.
Addressing the Federation of Small Businesses (FSB) in Manchester, Mr Miliband will say firms do not have the same level of protection as consumers.
He will promise to give business organisations like the FSB new legal rights to take cases - such as late payment by firms or government departments - to court on behalf of their members.
Mr Miliband will also announce measures including giving a new energy regulator powers to enforce a ban on suppliers from rolling firms over on to more expensive tariffs without their consent - or imposing retrospective back-billing for periods of longer than a year.