Ioannis Kouzis, associate professor at Panteion University's social policy department and adviser to GSEE, said the union's research suggested the jobless rate would hit 30 percent later this year.
"There are 470,000 households without anyone working," Kouzis told private Skai television.
"When the (austerity) measures started, unemployment was at 9 percent. Since then, incomes have been crushed and the official unemployment rate has reached 27 percent ... So the notion that lower salaries will boost employment has proved to be totally false."
Several hundred pensioners marched to the Labor Ministry in heavy rain to protest the new tax increases.
"We are not just talking about some problems. They are taking our lives away," Dimos Koumbouris, leader of Greece's main pensioners association, told the AP.
"We can't pay our electricity bills, or the emergency taxes. We haven't enough for our medicines, and it's putting our lives in danger."
Unions have called a general strike for Feb. 20, protesting the new tax hikes and a government decision to ax collective wage agreements in the public sector as part of an overhaul in pay scales for state-paid employees.
A furor has also erupted over whether there are plans to further reduce the minimum wage, which currently stands at just above â¿¬500 ($666) a month.
The government has come under attack from the main opposition Syriza party after Finance Ministry General Secretary Giorgos Mergos this week said the minimum wage "remains at high levels, and this is something we have to be careful of in our course towards development."
Syriza's youth wing briefly occupied Mergos' academic office earlier Thursday â¿¿ a common form of protest in Greece. The party accused the police of using force against the protesters.
The government has strenuously denied there are any plans to cut the minimum wage, or that this has been demanded by the country's debt inspectors.