Finnish Prime Minister Matti Vanhanen today warned that a dockworkers strike could have serious consequences if the industrial action is protracted, dpa reported. Some 2,500 dockworkers went on strike earlier Thursday after overnight mediation failed, with the action expected to affect 80 per cent of exports. Shortages of imported fruit and other fresh produce could also follow. The labour action had an immediate knock on effect as forestry and paper group UPM said it was forced to temporarily close its Rauma paper mill due to lack of warehouse space, impacting some 450 employees. The dockworkers strike was mainly over severance payment and redundancy terms as part of a collective agreement. National conciliator Esa Lonka was unable to present a compromise proposal between the Transport Workers' Union (AKT) and the Finnish Port Operators Association that groups 43 member companies in 25 ports. Lonka did not schedule a new meeting with the parties. Vanhanen, who was updated by Lonka, urged the parties to seek new talks, he told reporters. UPM said it was preparing for temporary shut downs at other paper mills and expected the last paper machine closures to take place early next week. The forest and paper industry on Wednesday warned of the negative effects of the strike. It was "threatening jobs in Finland and eroding Finnish factories' chances in international competition," Finnish Forest Industries Federation Chairman Kari Jordan said. The forestry federation estimated the costs at 30 million euros (40 million dollars) a day. Citing public interest, the labour minister in February ordered a two-week freeze on any labour action while the national conciliator was mediating in the conflict. The AKT union on Wednesday ended a day-long strike that impacted bus services in several cities and also regional bus links.