BRUSSELS (Reuters) - The European Union has resisted calls from some industries and countries to delay its flagship policy to fight deforestation, a letter seen by Reuters on Friday showed.

The deforestation law will, from Dec. 30, require companies selling soy, beef, coffee, palm oil and other products in the 27-nation bloc to prove their supply chains do not contribute to the destruction of forests. Equally, EU companies will be banned from exporting products cultivated on deforested land.

The U.S. government and industry groups including the Confederation of European Paper Industries (CEPI) want the policy delayed, citing complaints including that the EU's systems for managing the ban are not yet finished.

In a letter to CEPI members, dated July 2, European Environment Commissioner Virginijus Sinkevicius acknowledged such concerns but gave no indication that Brussels was considering a delay.

"We are hearing feedback from some stakeholders that preparation for implementation may be challenging. However, we also see encouraging signs in many sectors and countries working to align with EUDR (EU Deforestation Regulation) requirements," said the letter.

Sinkevicius said work on an online system to let companies submit their due diligence statements was underway.

Asked about the industry's concerns, CEPI Director General Jori Ringman told Reuters it was unfeasible for book publishers, for example, to trace the origins of their paper back to potentially thousands of forest plots.

"Neither the guidance nor the EUDR information system are ready," Ringman added, referring to the system that will allow companies to submit their due diligence statements.

The policy has split EU lawmakers and countries, with some supporting a delay, even after they approved the law last year with broad majority support.

Denmark's Environment Minister Magnus Heunicke this week wrote to the European Commission urging it not to postpone the world-first environmental policy - although he urged Brussels to quickly finish the technical systems needed to launch it.

"We are convinced that this regulation will be a genuine game changer in the global fight against deforestation," Heunicke said in the letter, seen by Reuters.

(Reporting by Kate Abnett; Editing by Gareth Jones)

By Kate Abnett