The number of Irish citizens on temporary visas in Australia has fallen by almost half in the past two years due to tighter immigration laws and shrinking job opportunities.
But an increasing number are deciding to stay on illegally after their visas expire because they cannot afford to move home.
"We are talking about the creation of a whole new undocumented section of Irish society in Australia now, and that is something we should be concerned about," according to Dr Mary Gilmartin, who lectures about Irish migration at the department of geography at Maynooth University.
She said a general tightening of immigration rules, and new caps on the number of skilled migration permits issued, mean it was “increasingly difficult to translate temporary visas into permanent residency” in Australia.
A total of 401 Irish citizens were “returned or removed” from Australia for violating the conditions of their visa in the 12 months to June 2015, a 37 per cent rise in the past two years.
Figures from the Australian Department of Immigration, released to The Irish Times, show that between July 2014 and June 2015, 92 Irish citizens were "removed" after being arrested and held at immigration detention centres.
A further 309 returned to Ireland voluntarily, after overstaying their visas and engaging with the immigration authorities.
Some received financial assistance to cover flights and other expenses, through the Australian government’s Assisted Voluntary Return programme.
Dr Gilmartinsaid: “By definition, it is very difficult to get a sense of an undocumented community, but that increase, as well as the anecdotal evidence from people in Australia, would suggest that many people are overstaying and spending many years undocumented without any sense of amnesty.”
It is likely that a large number of the Irish overstayers are working in construction, Dr Gilmartin added, as they were prioritised for temporary visas during the resources boom in Australia before the industry contracted and unemployment in the sector rose significantly in 2014.
Liz O'Hagan of the Claddagh Association (claddagh.org.au), a welfare group working with Irish people in Perth, said people are choosing to overstay because there is "a reluctance to return to Ireland for financial reasons".
“People cannot afford the resettlement costs,” she said.
Róisín Trainor of the Irish Australian Welfare Bureau in Sydney (iawb.org.au) said the organisation had assisted with several cases where Irish people were detained for overstaying, and "it has been highly stressful for those involved".
The overall number of Irish temporary visa holders has also dropped significantly. A total of 23,205 Irish citizens were in the country on temporary visas on 30th June 2015, down 44 per cent from the peak in the same month in 2013.
Just 5,221 Irish citizens were granted their first year working holiday visa in the 12 months to June 2015, down from 19,492 in 2011/12 when the number peaked.
The Department of Immigration figures also show a dramatic rise in the number of temporary visas held by Irish citizens cancelled before they expired, which Ms O'Hagan said reflected the large numbers of Irish construction workers on employer-sponsored visas being made redundant as the sector suffered further decline, particularly in Western Australia.
A total of 3,561 temporary visas, which includes working holiday visas and employer-sponsored work permits (called 457 visas), held by Irish people were cancelled in the 12 months to June 2015, up from 2,850 the previous year and just 985 in 2010/11.