Norske Skog, the world’s second-largest newsprint producer, faces a serious challenge this week from activist shareholders who want to break up the group.

Unionen – owned by prominent Norwegian investors Petter Stordalen, Øystein Stray Spetalen and Ove Gusevik – has called an extraordinary general meeting for Thursday to seek board representation. Unionen took advantage of the halving of Norske Skog’s share price over the past year to build up a stake of nearly 6 per cent, making it the largest shareholder.