More than 400,000 Victorians who run a small business or an Airbnb from the family home have been hit with hefty land tax bills for the first time as state government changes designed to try to rein in debt kick in.

The family home has always been exempt from land tax so long as business income derived from it is less than $30,000 – set by a ruling in 2012 – and the value of the property is below a certain threshold.