THE nation's competition watchdog is investigating possible breaches of competition laws in the fertiliser industry.

The Australian Competition and Consumer Commission would not confirm or deny that it is looking at the issue.

But it's understood the ACCC has been taking statements from relevant parties after being contacted by Liberal Senator Bill Heffernan.

The move comes amid allegations at a Senate inquiry last week that the National Australia Bank had refused to deal with independent fertiliser importer, Leighton Huxtable, because of pressure from an un-named fertiliser company.

Leading agri-business Elders was also the subject of allegations by Mr Huxtable, whose company, Direct Farm Inputs, is credited with forcing local fertiliser prices down.

Mr Huxtable told the inquiry the bank wouldn't deal with DFI because "it would appear some fertiliser company's been pretty heavy with the NAB".

Inquiry chair Senator Heffernan said he'd referred the issue to the "correct reporting authority" - understood to be the ACCC.

"My understanding is the state division of the bank advised you (Mr Huxtable) that the head office of the bank had advised them not to accept the business because of certain commercial reasons," he said.

"You've got it pretty right," Mr Huxtable said.

A NAB spokeswoman said the bank could not comment on loan applications because the information was confidential.

Mr Huxtable told the inquiry Elders had sacked the wife of his agent on Kangaroo Island - who worked as an Elders agronomist - "because of her husband's involvement with us."

He said Elders had offered her her position back "providing her husband withdraw all association with DFI".

Elders Rural Services managing director Mike Guerin confirmed the sacking, saying it was prompted by a breach of company policy.

"Specifically, where employees have an obvious conflict of interest, it must be declared and in this case it wasn't," Mr Guerin said.

"We acted in accordance with industrial relations requirements and internal policy."

Mr Huxtable also said a DFI customer had told him a finance company - "you mentioned Elders before, so I'll mention them" - had refused finance to buy DFI fertiliser "but would write an order out straight away if they bought through them".

Mr Guerin said Elders, "like any other business like ours", offered finance to farmers buying from the company.

"We don't fund our competitors' retail activity in the same way that they don't fund ours,"he said.