"As far as Athens is concerned, I also think about all those people who are trying to escape tax all the time," Lagarde was quoted as saying in Saturday's Daily Telegraph.
"And I think they should also help themselves collectively [by] paying their tax," she said in an interview.
Greece's central bank has said unpaid taxes come to between 2.5 percent and 3.8 percent of the country's gross domestic product.
The country's so-called "shadow economy," comprised of business transactions that do not include tax payments, came to 25.4 percent of the country's GDP in 2010, up from 24.3 percent in 2008.
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