Nearly 200 staff at George Calombaris' restaurants have been underpaid $2.6 million, with the celebrity chef blaming "historically poor processes" for the bungle.

Calombaris underpaid 162 of the 430 current staff at restaurants including The Press Club, Gazi and Hellenic Republic, which form part of the chef's Made Establishment Group, over the past six years.

Staff were not paid the correct salaries or overtime due to the "poor processes in classifying employees", Calombaris said.

Employees at his Greek street food restaurant chain Jimmy Grants were not affected, he said.