The EU's deforestation law will, from Dec. 30, require companies and traders placing soy, beef, coffee, palm oil and other products on the EU market to provide proof their supply chains do not contribute to the destruction of forests.

In a statement published on Thursday, EU lawmaker Peter Liese - environment spokesperson for the European People's Party (EPP) lawmaker group, which is von der Leyen's political group - urged the European Commission to delay and then scale back the law, which he called a "bureaucratic monster".

"Many small farmers around the world and even small forest owners in the European Union cannot work with the text," said Liese.

EU leaders are expected to endorse von der Leyen for a second term as Commision president at a summit on Thursday.

But she still needs backing from half of lawmakers in the newly-elected European Parliament. That will require winning support not only from the EPP, but also from groups including the socialists, who are pressuring her not to water down environment policies.

A source in the Socialists & Democrats (S&D), the second-biggest lawmaker group in the European Parliament behind the EPP, said the S&D was "totally opposed" to delaying the deforestation law.

"It is a clear no go for S&D. The Commission has an obligation to implement it," the source told Reuters.

Green lawmakers - whose support von der Leyen may also need to win a comfortable majority - are also opposed to any delay and seeking assurances from von der Leyen that she will continue Europe's climate agenda.

The European Parliament negotiated and approved the EU deforestation policy with a large majority last year - 552 votes in favour, versus 44 against and 43 abstentions.

But the policy has come under fire from some industries and the U.S. government, which last month asked the EU to delay it, a letter previously reported by Reuters showed.

A European Commission spokesperson said it was working to ensure all the conditions are met for a smooth implementation of the deforestation rules.