Self-funded retirees Vincent and Judy Mahon are unusual among the hundreds of people who have made submissions to a parliamentary inquiry into Labor's proposed franking credit changes.

The two have a self-managed superannuation fund (SMSF) and will suffer a drop in income if franking credits become non-refundable. But they insist the "taxpayer-funded largesse" inherent in the system is unsustainable and inequitable.