The tax rate for Greeks earning more than $56,000 -- considered the highest income bracket -- will be 42 percent, the BBC reported Saturday.
The tax measure was pushed by the conservative coalition government, which set a target of raising $3 billion during the next two years, Ekathimerini reported.
During debate on the measure, leftist Member of Parliament Panayiotis Lafazanis called Finance Minister Yannis Stournaras a "political terrorist."
The comment and others from members of the SYRIZA party undermined efforts by the left to raise its stature in the eyes of the international community, government spokesman Simos Kedikoglou said.
"As much as the SYRIZA leader (Alexis Tsipras) tries to appear like a European by talking about serious foreign investments, he is disrobed by the actions and comments of his deputies," Kedikoglou said.
Tsipras -- who is scheduled to meet with German Finance Minister Wolfgang Schaeuble in Berlin Monday -- said: "The Germans are very practical people. They can see that SYRIZA could be the next government and they want to prepare the ground by having direct contact with us. We want the same.
"What we need are solutions," he said. "SYRIZA wants to have normal relations with the governments that play an important role in Greek and European affairs."