Sofia - Bulgaria is set to step up labour controls in order to curb the economy's booming unregistered labour sector and boost dwindling budget revenue, the country's labour minister, Totju Mladenov, said Monday.

There are some 400,000 people working in Bulgaria's "black labour market," according to the government. In comparison, at the end of 2008, there were 2.4 million registered employees in the country.

Stricter controls are aimed against employers who fail to register their workers and thereby avoid paying insurance and other mandatory dues. This widespread practice has helped push the national social- care institute to run a 558-million-leva (404-million-dollar) deficit, Mladenov said.

Prime Minister Boiko Borisov's ruling conservative coalition, in power since last month, is threatening a 15,000-leva fine for each unregistered worker.

The authorities, aiming to boost revenue and keep the budget deficit at 2.5 per cent of the gross domestic product, have already stepped up controls on the borders and produce markets. (dpa)