The test ballot - a non-binding vote - showed 56 'no' votes and 4 abstentions on Tuesday.
Talks between Greece and its international creditors on a third bailout began in Athens.
Euro zone leaders made Greece surrender much of its sovereignty to outside supervision on Monday.
Thomas Piketty is calling out Germany, describing the country's strident moral position on Greece's debt as hypocritical and a "huge joke."
Merkel has long said she wants to see Greece remain in the eurozone, but "not at any price."
Yanis Varoufakis, Greece's flamboyant finance minister, abruptly resigned Monday morning despite a national referendum that delivered a rousing endorsement to his anti-austerity policies just hours earlier.
The resounding rejection of an international bailout deal by voters in Greece raised fears Sunday of the collapse of the country's banking system, a catastrophic government default, an eventual exit from the euro and potential ...
Many Greeks fear EU leaders' warnings that a "no" vote could mean Greece's exit from the euro -- a Grexit.
A last-minute request by Athens for an extension of its current bailout, which expired late Tuesday, was rejected by the other 18 nations that use the euro currency.