Larry Anthony is the executive director of SAS Consulting Group, but he has not been listed on the lobbyist register since he became the Nationals president in 2015.
This year, Santos and Delta Electricity became clients of SAS Group, as first reported by Fairfax.
The Federal Government had threatened to restrict companies, including Santos, from exporting gas — before it struck a deal with them this week to adequately supply the domestic market.
Delta Electricity has flagged plans to expand its electricity production in Australia.
Mr Anthony has not responded to the ABC's requests for a comment, but in a statement, SAS Group said it always operated, "in accordance with the federal lobbying laws and code of conduct and we will always do so".
"We note that the Fairfax journalist has made no allegation of impropriety, and was not able, when asked, to point to any breach of the relevant code," the statement said.
"We are unbothered by the baseless implications upon which the news story is founded.
"However, we are deeply offended that our hard-working staff and consultants should have their achievements debased in this way."
There has been bitter infighting within the Coalition about the future of renewable energy in Australia and new reports predict a gas shortfall next year could be three times worse than expected.
Financial institution Indue Limited, which is operating the Government's cashless welfare card, is also a client of the SAS Group.
The program is being trialled on Centrelink recipients in four locations around the country and quarantines a large chunk of welfare payments and cannot be used to pay for alcohol or gambling.
The Federal Government is not ruling out extending the controversial card, as Nationals MPs push for a widespread roll-out.
Mr Anthony was a Howard government minister and held leadership positions predominately in the social security portfolio.