Sisak's 60,000 barrel-per-day (bpd) refinery is owned by Croatian energy firm INA which is in turn owned by the Croatian government and Hungary's MOL.
INA, which also owns a bigger refinery with a 100,000 bpd capacity in the northern Adriatic city of Rijeka, said last week it planned to close the fluid catalytic cracking facility (FCC) in Sisak to make better use of facilities in both refineries.
It said that the measure would cut 40 jobs in the second half of this year, but trade union representatives for the Sisak refinery said they feared it was the first step towards the closing down the entire plant.
"The workers hit by this measure would be offered adequate other jobs in the refinery," Plenkovic told a cabinet session.
Zagreb, which owns close to 45 percent of INA, and MOL with an almost 50-percent stake, have for several years been at odds over management rights and INA's investment strategy. Croatia said it wanted to buy back INA's shares from MOL which MOL accepted but said the price must be adequate.
The future of the Sisak refinery was one of the bones of contention between the two shareholders as Zagreb primarily focused on saving jobs rather than profitability. A recent study by Deloitte proposed converting the refinery into a logistics centre and a facility to refine biomass.
The Croatian government is in the process of choosing an adviser for buying back INA shares from MOL and for potentially seeking another strategic partner.