"The Greek finance minister approached me," Widmer-Schlumpf said. "We are conducting technical discussions. I am not able to give you an indication of the sort of volume we are talking about," she added.
One of the main problems in debt-wracked Greece is the difficulty authorities have in collecting taxes.
Earlier on Wednesday, Germany and Switzerland clinched a double-taxation deal that aimed to draw a line under a prickly tax evasion dispute between the two European financial centres.