France and Ireland say they will not ratify a huge trade deal with South American nations unless Brazil does more to fight fires in the Amazon.
French leader Emmanuel Macron said President Jair Bolsonaro had lied to him about his stance on climate change.
There are currently a record number of fires in the Amazon rainforest - a major source of oxygen for the world.
Environmental groups say the fires are linked to Mr Bolsonaro's policies, which he denies.
European leaders have also expressed dismay over the fires, with UK Prime Minister Boris Johnson saying he is "deeply concerned" about "the impact of the tragic loss of these precious habitats".
German Chancellor Angela Merkel has called the fire an "acute emergency... shocking and threatening not only for Brazil and the other affected countries, but also for the whole world".
Mr Bolsonaro said on Friday that he was considering options for fighting the fires, including deploying the military.
However, he has also accused Mr Macron of meddling for "political gain", and previously said calls to discuss the fires at this weekend's G7 summit in Biarritz, France - which Brazil is not participating in - showed "a misplaced colonialist mindset".