Government MPs have questioned whether the South Australian could be in breach of the constitution over his ties to the gym.

The Australian reported on Tuesday that Australian Securities and Investments Commission records show Mr Zappia was a partner in the Funlife Fitness Centre from April 1983 until June this year.

Funlife offers clients services through Medicare, the National Disability Insurance Scheme and the Department of Veterans' Affairs.

A spokesman for Mr Zappia said he ceased to have any interest in Funlife Fitness Centre "many years ago".

"However, the ATO was only advised of this recently, due to an oversight by his accountant's office," the spokesman said in a statement.

"Tony does not receive any income from this business."

Section 44 of the constitution disqualifies anyone who has a "direct or indirect pecuniary interest" in any agreement with the Commonwealth.

In his member's register of interests, Mr Zappia declared his wife received substantial income from the fitness centre.

Mr Zappia won 10 Australian powerlifting championships during his 18 years competing in the sport.

Home Affairs Minister Peter Dutton and fellow Liberal MP Chris Crewther could face High Court referrals over eligibility questions if Labor wins enough crossbench support for the move.

Australian Associated Press