The review will seek to determine whether the planned aid will enable the company to become viable without continued public support and whether the owners contributed sufficiently to the cost of restructuring, the Commission said Wednesday.

In July the Commission provisionally cleared the aid subject to a commitment by Slovenia to notify a restructuring plan capable of ensuring the long-term viability of the firm.

In November 2013, Slovenia submitted the restructuring plan, which is based on a debt-to-equity conversion of the state's claim against the company, but the Commission now said it had "doubts whether the plan complies with the requirements".

The Commission is "concerned that the company owners may not sufficiently contribute to the restructuring cost," as funding designated as own contribution by the company may actually come from state resources and involve additional state aid.

Furthermore, the forecasts of the company's long-term viability may not be realistic and the proposed capacity reduction may not be adequate to compensate for the distortion of competition.

The news comes three weeks ahead of a Cimos shareholders' meeting at which a proposal to convert between EUR 112m and EUR 186m of debt to equity will be put to a vote.

Cimos, which employs 7,000 workers, declared insolvency in early March. The business daily Finance has reported that the group's outstanding financial debt is about EUR 400m.