The entrance to the company, located in the town some 60 km southeast of Zagreb, was blocked for some time, but production was unobstructed, witnesses said.
Officials at the Sisak County Prosecutor's Office said that the Office of the Chief State Prosecutor was not involved in the operation and that the police were conducting an investigation.
It is assumed that the police investigation has to do with disputes regarding the privatisation of Gavrilovic over which the company's owner, Austrian national Georg Gavrilovic, has sued the Croatian state seeking 300 million euros in damages.