Agriculture is one of the biggest industries in Cumbria and the south of Scotland - employing more than 10,000 people.
of Britain's food exports from agriculture go to EU countries.
Between £2.5bn and £3bn in EU subsidies is given to British farmers.
More than 50% of all farm incomes in Britain, come from these EU subsidies.
Those who want to stay in the EU argue that all the subsidies could be lost if we leave. But Leave campaigners say if we weren't paying for EU membership, there'd be plenty of money left over to help farmers in need.
The NFU and its counterpart in Scotland have now also decided that members would be better off remaining in the EU.
Robert Craig, a former chairman of the NFU in Cumbria, says after wavering he's now decided to vote to remain in the EU:
I feel from the indication we're getting from DEFRA that we're not prepared to be in. It seems there isn't a real contingency being even looked at so far as government is concerned.
Ed Studholme, at Great Orton near Carlisle, is convinced that leaving the EU would be best for farmers:
As any small business we find that bureaucracy is increasing, whether that's from government in Westminster or government in Europe. I think more fundamentally for me we need less government, not more.
For all farmers, and those in the wider agricultural industry, the stakes are potentially very high and the outcome could affect their businesses for decades to come.