At least three labor ministry officials are believed to have manipulated data for a monthly labor survey and failed to report it.
The revelation is the latest development in a widening scandal over the ministry's regular survey on wages and working hours that stretches back to 2004.
Sources say that from January last year, the head of the office in charge of the survey and two other officials began adjusting the data.
The sources say the officials failed to report what they were doing to their superiors.
The changes they made weren't published until after the scandal first came to light.
The three officials reportedly told an investigative panel that they had no intention of covering up what they did.
The panel plans to publish a final report on the matter as early as next week.