The wet weather has made it "nearly impossible" to spread slurry safely on many farms across Northern Ireland and farmers are concerned as the closed period deadline has passed.
A ban on slurry spreading came into effect at the weekend and will last until February.
But the situation has been described as "very stressful" due to the ground and weather conditions since summer.
Farmers have been urged to use the ‘reasonable excuse’ clause if they are forced to spread when conditions are not suitable.
It covers exceptional circumstances when, through no fault of their own, farmers cannot fully comply with the rules.
“The reasonable excuse clause is as a last resort. No farmer wants to risk their basic payment by spreading slurry during the closed period,” explained UFU President Barclay Bell.
“However, the current ground and weather conditions are making compliance impossible and some farmers may be left with no other choice. It is better to spread slurry during the closed period under this clause at a time when conditions are more favourable than rush and risk a farm accident or pollution.”
The slurry ban is an EU rule intended to protect the environment by limiting the spread of slurry during winter months when grass growth is limited and nutrient uptake is low.
Mr Bell said that EU Commission officials are keeping a close eye on Northern Ireland in relation to the current rules.
They have scrutinised the monitoring of spreading practices and water quality data.
Mr Bell continued: “We do not want to give the EU Commission any excuse to impose more legislation. Being able to show we acted responsibly in these difficult conditions is our best defence.
“I would, however, encourage the EU Commission and government authorities to be mindful of the stress farmers are currently under.
“Farmers are the first friends of the earth and since the introduction of the closed spreading period we have made every attempt to comply with the regulations. However, farming by calendar dates poses a real challenge when it comes to the practicalities of running a farm and unpredictable weather.”