In its new report, Farm Broadband and Mobile Networks, the union said roll-out of complete mobile networks and affordable reliable superfast broadband to rural areas must be prioritised.
The document is based on a survey of farmers and growers.
Only four per cent of farmers have access to superfast broadband but, the report said, farmers need quality broadband and mobile network to run safe and efficient farms, comply with regulation, promote farm diversification and enjoy family life.
The NFU is calling on the Government to provide the funding, legislation and business support which will enable this.
It is concerned the Government’s £1.7billion broadband delivery programme will leave an estimated 1.2 million premises without superfast broadband; five per cent of all premises. The majority of these will be farm businesses and rural premises.
At best, farmers in this last five per cent could be offered far lower speeds of 10 megabits per second by 2020, whilst other industries and urban areas receive superfast speeds of 30Mbps or ultrafast speeds of 100Mbps plus.
NFU vice president Guy Smith said: “If our industry is to meet any of the ambitions of the long awaited government 25-year food and farming plan, it will be essential for barriers to growth to be removed. Poor access to broadband and mobile networks is one such significant barrier and the current situation is neither sustainable nor acceptable.
“The Government is asking farmers to run their businesses in conditions that put them at an immediate disadvantage.”
Mr Smith said farmers could not comply with increasingly online only regulation and were not able to contact their customers.
“Farmers can’t harness the brilliant range of agri-technology which relies on a reliable internet connection” he added.
“To increase productivity you need superfast broadband, to get out of the farm office and into the field.
“Well over half of our members have diversified their farm businesses with the aim of supporting the wider rural economy, but they simply won’t be able to support this wider economy if they can’t offer high-speed broadband.”
Digital Economy Minister Ed Vaizey said improving mobile coverage and taking fast broadband to rural areas was one of the Government’s top priorities.
"Nine out of ten homes and businesses in the UK can now get superfast broadband, with thousands more being reached every week," he said. "
"We are offering immediate assistance to those with the slowest speeds with our satellite broadband scheme and our plans will give every farm in the UK the legal right to request a fast broadband connection."