The Home Affairs Department predicts proposed changes to Australia's character test will mean more migrants will be deported - but is unable to estimate how many.
The Home Affairs Department can't say how many migrants they expect to fail the character test under planned changes to make it easier to deport foreign criminals.
Department officials were grilled by a Senate inquiry about government plans to lower the bar for criminals' visas to be cancelled.
Under the proposed laws, non-citizens convicted of a crime that carries a maximum sentence of at least two years would automatically fail the character test, regardless of whether they are sentenced to any jail time.
Assistant Secretary Michael Willard said that would provide a clear standard of behaviour for visa holders.
Labor Senator Kim Carr repeatedly asked how many more foreign criminals would face deportation under the new regime, compared to the current deportation rules which apply to visa holders sentenced to 12 months or more in jail.
Mr Willard told the committee in Canberra they expected an increase, but couldn't provide an estimate.
"The department's had look at a number of sources to determine what the total affected number of people may be, however providing an exact figure is not possible," Mr Willard told the committee.
Senator Carr said he was surprised the department had "nothing to go by" given the new rules were designed to be an "objective" measure.
Migration experts have predicted a five-fold increase in the number of migrants who would fail the character test after examining crimes covered by the proposed laws such as common assault which rarely results in a jail sentence.
Mr Willard rejected claims from opponents of the bill that changes were not necessary as the government already has additional powers to kick out someone deemed a threat to the community.
He said some decisions using those provisions had been successfully appealed by foreign criminals in the past.
He referred to one case of a man who had a bridging visa and had applied for permanent residency, who was convicted of stalking his partner and threatening to cause her serious injury.
The government cancelled his visa, but it was reinstated upon appeal, allowing him to stay in Australia.
In another example, a Queensland man who was given a two-year good behaviour bond for sexual offences did not meet the threshold for deportation.
But under the new regime, he would automatically fail the character test as the offences carried a maximum penalty of 14 years jail.
Department officials also refuted suggestions by lawyers and refugee groups that victims of domestic violence could be penalised for aiding and abetting the breaking of a protection order, arguing such an incident was unlikely to be prosecuted.
Earlier, New Zealand High Commissioner Dame Annette King told the committee the proposed laws would make bad legislation even worse.
She said changes made to deportation laws five years ago had disproportionately affected Kiwis.
"The 2014 changes have been corrosive to our New Zealand-Australia relationship," she said, echoing NZ Prime Minister Jacinda Ardern.
She said low rates of dual citizenship meant New Zealanders, including children, living in Australia were more vulnerable to deportation policies.
"This is one area where we do see it eats away at the people-to-people relationship," Dame Annette said.
New Zealand would like special consideration under a ministerial direction, as recommended by parliament's migration committee.
The committee is expected to hand down its final report on 13 September, before the Senate considers the legislation.