Declan Ganley is likely to have to prove to the State ethics watchdog that his €200,000 'loan' to his Libertas lobby group is genuine and not a donation.
The multi-millionaire businessman gave the first indication of the source of Libertas's lavish spending on the Lisbon Treaty referendum when he admitted to the loan.
The electoral laws may be lax on the level of scrutiny of non-political party groups, such as Libertas, involved in campaigning, but there are tight rules on loans.
A loan must be a written agreement with the terms and conditions applying to it and the repayment stated clearly. Interest must be charged at the same rate levied by the financial institutions and if the interest is lower than the commercial rate, the difference is regarded as a donation.
The loan revelation was noticed by the Standards In Public Office Commission, which polices spending and donations by political parties and groups.
The Commission does have the power to ask to see all the relevant documentation.
Libertas has repeatedly said it is fully aware of the ethics laws and abides fully by the regulations. And there is no evidence to suggest the group has not been complying with the legislation.
Given the Commission's status as the ethics watchdog and the amount of controversy over the funding of Libertas, the group is highly likely to either volunteer details of the loan or else be asked for it.
The Commission does not comment on individual cases or what action it might take if it has a query.
"We are aware of the media coverage raised around Libertas. We have the power to make whatever inquiries are necessary. We have guidelines on loans and these would apply to a third party," a spokesman said.
The Commission also says the question of a loan being given to a politician or organisation has never come up before.
"It's uncharted water," a spokesman said.
Meanwhile, another high-profile, wealthy businessman says he did not give any loans to Libertas.
Aviation millionaire Ulick McEvaddy said he merely gave a small financial contribution of several hundred euro and no loans. "No. And I am not a member of Libertas," he added.