(Bloomberg) -- Naturgy Energy Group SA’s biggest shareholder rejected IFM Global Infrastructure’s 4.9 billion-euro ($5.8 billion) offer for almost a quarter of the Spanish utility.

Criteria Caixa, the Spanish holding company that owns more than 26% of Naturgy, said IFM’s offer doesn’t fully satisfy its interests, according to a statement late Thursday. Naturgy’s board said last week the offer was “reasonable.” 

IFM initially offered 23 euros a share for a nearly 23% stake stake in Naturgy in an unsolicited bid in January. It later adjusted the price to 22.07 euros to take into account dividends paid in the interim. 

Criteria Caixa, which manages the investments for Barcelona-based CaixaBank SA Foundation, said in May it planned to increase its stake in Naturgy to keep the company listed in Spain and to ensure the country’s energy security. It had a 25% stake at the time.

The government in August approved IFM’s bid, but attached conditions including commitments to keep the utility’s headquarters and a large part of its staff in Spain. 

A successful bid will give IFM a similar-sized stake to that of existing shareholders Global Infrastructure Partners and CVC Capital Partners-backed Rioja, which have said they won’t sell their stock. A potential alliance of those three international investors could pit them against Criteria Caixa.

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