The NFU is seeking clarification from the BBC over impartiality after Chris Packham posted strong views calling for a ban on glyphosate.
The Springwatch host took to Twitter to urge his followers to sign a petition to ban the weedkiller.
Mr Packham also tweeted a link to a report by the Ethical Consumer website and magazine, which is highly critical of the NFU.
The NFU said the report was “riddled with inaccuracies and out of date information”.
The report, written by a group which has spoken out against the badger cull and urged shoppers to boycott dairy products, also brands the NFU as an “anti-environmental lobby group”.
— Chris Packham (@ChrisGPackham) February 12, 2017
An NFU spokesman said: “We have written to the BBC to express our concerns about Chris Packham’s comments to get a clear understanding of its position in employing someone who clearly has very strong views on issues, but is consistently portrayed as an impartial expert.”
Commenting on Mr Packham’s glyphosate tweet, the NFU said regulatory bodies around the world had concluded it poses “little or no risk to people in their everyday lives when used correctly”.
The NFU spokesman added: “Debates about the future of products like glyphosate need to be based on science and evidence, not on the opinions of people who dismiss information that doesn’t support their position as ‘industry propaganda’.”
Farmers also hit out on Twitter to criticise Mr Packham over his stance on glyphosate.
Yorkshire farmer and Club Hectare co-founder Jono Dixon (@sunkfarmer) tweeted: “The birth control pill is more dangerous than #glyphosate as is toothpaste. Packham you buffoon do ya homework.”
Leicestershire grower Keith Challen (@keithchallen) said: “Chris Packham your irresponsible statement will lead to harming the very things you wish to protect! #factsnotfiction”
Frustrated former NFU president Peter Kendall (@pkendallfarm) wrote: “And he’s still being employed by the BBC.”
BBC – personal views
It is not the first time that Mr Packham has used his public profile to make statements in support of causes he feels strongly about.
Last year, he was investigated and cleared by the BBC Trust following a complaint by the Countryside Alliance that he had breached corporation guidelines on bias after he described people involved in hunting as the “nasty brigade”.
Mr Packham has previously branded those carrying out the badger cull as “brutalist, thugs, liars and frauds”.
Last month, he was forced to post a clarification on his Twitter account apologised after posting an inaccurate tweet that farmers were shooting lapwings.
A BBC spokesman said: “Chris Packham is a scientist and naturalist in his own right and is not solely employed by the BBC.
“Chris’s personal social media accounts are not connected to his work as a BBC presenter and we are confident that our audience recognise that these are his personally held views as a naturalist expressed on his own Twitter account.”