They are giving the government a three-week ultimatum to grant them permits, or else warned it will have to tackle a health disaster.
The immigrants – who have been employed in menial jobs across Greece -initially occupied the first floor of the law faculty at the University of Athens for five days.
They were subsequently moved to a private building rented by pro- migrant campaigners following a stand-off with police.
The protesters refused tea and sugar on Tuesday. Their appeal for legalisation has been rejected by the Socialist government as it tries to deal with the growing problem of illegal immigration.
“We will continue our fight until the end,” said one immigrant during a press conference.
Student and immigrant rights groups said the protest was intended to draw attention to the increasing number of similar strikes currently underway across the country.
In a separate incident, seven Afghan refugees sewed their mouths shut to protest the slow pace at which their asylum applications were being processed by the Greek authorities.
Ill-treatment
They were following the example of a group of Iranians who managed to secure refugee status after adopting the same tactic.
The European Court of Human Rights recently fined Greece and Belgium for their ill-treatment of an Afghan refugee who claimed to have suffered abuse in both countries.
Greece has been repeatedly criticised for being one of the European Union countries that grants the smallest number of asylum pleas.
Thousands of refugees trying to make their way into Europe have ended up being stranded in Greece, as the country struggles to cope with a financial crisis and a huge backlog of asylum applications.
More than 128 000 migrants, or roughly 400 a day, entered the country illegally in 2010, according to government figures.
The measures the government has proposed to crack down on illegal immigration include the construction of a 12.5km-long fence along a section of the Greek-Turkish border; floating prisons; and using old army bases to detain illegal immigrants.
Source: news24