Electoral authorities are examining an offer by an Adelaide businessman to donate $500,000 to the Liberal Democratic Party in return for a guaranteed position as the party's lead Senate candidate in South Australia.

The Australian Electoral Commission said it was "concerned" about a written agreement, revealed by Fairfax Media, in which property developer and former abattoir owner Roostam Sadri indicated he was willing to fund the party in return for a start in politics.

On Tuesday, a spokesman for the AEC confirmed the matter had been referred to the Australian Federal Police for investigation.