Greece will screen immigrants living in the country to determine who is entitled to asylum and expel those who break the law, a junior minister said on Saturday.
"The people who meet the conditions for return will return home," deputy labour minister Anna Dalara told Flash Radio.
"Whatever the case, if there is law-breaking behaviour they will receive their tickets and they will leave," she said.
Greek authorities say a surge in arrivals by thousands of would-be immigrants and asylum seekers has stretched the country's capacity to breaking point.
The Socialist government recently announced plans to erect a 12.5-kilometre (eight-mile) wire fence along a stretch of its northeastern border with Turkey that is commonly used by traffickers to deposit their human cargo.
Athens has also pledged to step up asylum examinations to clear a backlog of some 47,000 applicants, many of them awaiting approval for years.
Rights groups have repeatedly criticised Greece for failing to provide adequate shelter and support to people fleeing conflict in Africa, the Middle East and the Indian subcontinent.
Would-be immigrants and asylum seekers are currently kept in squalid and congested detention centres and police cells for months.
Most are then released with an administrative order to leave the country. Some try to book illegal passage to other European countries but the majority end up on the street, destitute and at risk from criminal gangs.