A high-profile fund manager leading an assault against Labor's changes to franking credits once boasted about using a taxpayer-funded inquiry to maximise the chances of defeating the policy.

In an audio recording obtained by The Sydney Morning Herald and The Age, veteran fund manager Geoff Wilson claims he contacted Liberal MP Tim Wilson to ask for parliamentary hearings into Labor's proposed changes to be scheduled at the same time as of one his own six-monthly investor roadshows.

Geoff Wilson, left, and Liberal MP Tim Wilson, right, are related. Credit:Dominic Lorrimer/Alex Ellinghausen

Tim Wilson, who is chairing the probe into Bill Shorten's plan to rein in franking credits, is also an investor in funds run by Wilson Asset Management, a firm founded and chaired by Geoff Wilson with $3 billion in funds under management.

The MP has disclosed the shareholding in the parliamentary register but has not declared it during public hearings around Australia. That is a departure from a standard set by Liberal MP David Coleman, who regularly declared his interests in a financial services firm during a recent banking inquiry.