UPM's John Sanderson, director of environmental affairs for the UK, said the initiative was a valuable addition to improve its understanding of sustainable paper consumption.
"There is a clear need for a balanced view on this topic," he said.
The campaign aims to dispel environmental misconceptions around print and paper.
Martyn Eustace, who is heading up Two Sides for the NAPM, said the campaign now has "all the major mill and merchant groups", as well as growing support from others involved in the supply chain.
This includes Sun Chemical, Fuji, Haymarket Publishing, Duplo and Trinity Mirror Printing.
In October, the NAPM launched Two Sides to show that print and paper is an environmentally sustainable medium.
Printers can join the campaign for £25 per million of UK turnover, although there will be a minimum of £150.
In November, Stora Enso and Sappi pledged their support for the campaign.
UPM welcomes 'balanced view' of Two Sides initiative
Paper giant UPM has joined Stora Enso and Sappi in its support for the Two Sides campaign launched by the National Association of Paper Merchants (NAPM).
