Workplace inspections by labour authorities showed the rate of illegal employment reached 13.62 percent in January-September last year, a report by the finance ministry shows.
The rate was about two percentage points higher than in the same period a year earlier.
Fully 38 percent of the illegally employed worked in the construction industry.
The rate of illegal employment was also high in the catering industry.
Inspections were carried out at 13,316 employers with more than 54,000 people on payroll during the period.