The proposed action follows 12 days of separate pay negotiations by Finnish Paperworkers' union Paperiliitto, representing 16,000 blue-collar workers, and white-collar workers' union Proliitto with the Finnish Forest Industries Federation (FIFF).

Paperiliitto agreed terms with FIFF on 16 March for a guaranteed 2.5% (EUR 0.41 per hour) increase; however, it refused to offer the same national pay deal to Proliitto, stating that wage hikes would only be negotiated on a mill-by-mill basis.

According to the International Federation of Chemical, Energy, Mine and General Workers' Unions (ICEM), the stand-off "quickly became an insult to [the white-collar] staff".

A strike notice was issued on 23 March, with an overtime ban due to begin on 1 April and a full strike to follow from 6am on 6 April at all UPM operations if official government mediation fails.

Dick Blin, pulp and paper officer at ICEM, said: "In order for a strike to be prevented, FIFF will have to put an acceptable national wage offer on the table on 4 April. Otherwise, 1,000 white collar workers at UPM mills will take decisive industrial action.

Tripartite negotiations between the employers, Proliitto and government mediators on the crucial wage offer will be held at 4pm on Monday (4 April). Blin said that the employers' insistence that wage negotiations be carried out at local level was "unacceptable to the union".

UPM was unavailable for comment at the time of writing.