The 3,500 people on the payroll of energy company Eneco have published an open letter to their shareholders warning about the consequences of selling their shares.

Eneco’s shareholders are 53 local authorities – including Rotterdam and The Hague – who must decide before 31 October whether to hang on to or sell their shares in the utility.

Most of the shareholders have tiny 1% to 2% stakes in Eneco and a sale would raise an estimated €3bn – which many could use. But a sale risks putting the electricity company into the hands of a new owner who would not continue Eneco’s current policy of sustainability as well as providing job security, the letter stresses.

The letter, sent in the name of the company’s works council,  was sent to 1,200 council members in such places as Dordrecht, Delft, Amstelveen, Aalsmeer and Ameland.

About a week ago, Rotterdam with a 32% shareholding in Eneco – the largest – voted to sell its shares. But The Hague, number two with 16%, decided to hang on to theirs. At present shareholders representing only about 25% of the shares are expected to favour remaining an owner.

Eight years ago, the two other main energy firms Nuon and Essent were also sold off, each for around €9bn. Nuon is now owned by Swedish state owned firm Vattenfall while Essent is the hands of German utilities group RWE.

Eneco is a much smaller firm, serving only 3.5 million Dutch households.