It follows reports that the Government is considering extending the numbers of people who pay PRSI, as part of plans for a new unified social insurance payment or Universal Social Contribution.
Paddy Keating of IMPACT said the most important aspect of any extension of the social insurance contribution system is that it is fair, and that it takes account of peoples' ability and inability to pay.
He said the Government must also take into account the connection between social insurance contributions and entitlement to benefits when devising the new scheme.
Mr Keating said there was no justification for not applying PRSI to other non-earned income like share options and rental income, provided it was done on an equitable basis.
But the organisation representing landlords said it opposed any plans to extend PRSI contributions to rental income, saying landlords were already at the pin of their collar.
The Irish Property Owners Association said any new costs would drive more landlords out of business, reducing the stock of rental housing in the market.
The Small Firms Association (SFA) said it would be concerned about any plans to charge PRSI on share options or investments, saying great progress had been made on the tax treatment of such employee incentives in recent years.
But acting director Avine McNally said the SFA would welcome an increase in the PRSI contribution rate for the self-employed, providing it meant self-employed people were entitled to the same benefits as everyone else.
