NFU Cymru has asked the Welsh government to make an early commitment to maintain the Basic Payment Scheme in Wales for 2021.
It comes after Welsh officials announced last year that the BPS would remain unchanged in 2020.
However, the uncertainty in the intervening period has only intensified, NFU Cymru points says, and a no-deal Brexit now appears to be a 'very real possibility'.
Because of this, the union's president John Davies has asked the Welsh government's rural affairs minister, Lesley Griffiths, to commit to maintain the BPS unchanged for 2021.
Mr Davies said: “There are many factors completely outside of our control which considered individually or collectively would have a very detrimental impact on Welsh agriculture.
“NFU Cymru is of the view that this calls for a cautious and restrained approach from Welsh government when it comes to developing future agricultural policy.
“We would urge government to take its time and not to hasten to move away from the present arrangements until we have a far clearer picture of the sort of future trading relationship we will have with the EU27.”
In addition, NFU Cymru has asked Ms Griffiths to ensure that the additional £5.2m per year for the next two years made as part of the UK government’s response to the Lord Bew review last month is used as a top up to the BPS.
This funding has been allocated to Wales because average Pillar 1 payments have historically been lower in Wales than in some other parts of the UK.
“We therefore firmly believe that as the Lord Bew review was about correcting this matter then the additional money should be made as a top up to the BPS and not spent elsewhere,” Mr Davies said.