UP to 15,000 farmers have marched through Dublin demanding that the Government take a hard line in negotiations on the next round of European subsidies.
John Bryan, IFA president, said failure to return the €1.6 billion package would be bad for the industry and undermine the viability of the most productive farmers.
"The next two months will see decisions taken in Brussels and by our Government that will have a huge bearing on the ability of the sector to survive and grow. Farming can help deliver recovery and jobs but only with the right policies and supports," he said.
"Farm output will drop and the raw material for our ambitious growth plans will not be available if the EU Commission gets its way."
The Day of Action, involving bus-loads of farmers from all over Ireland, saw a march from Merrion Square to Stephen's Green and on to Leinster House for a rally.
A convoy of farming vehicles and tractors drove down Kildare Street as thousands of farmers flooded the narrow street.
A Garda spokesman estimated that around 15,000 people took part in the march, along with about six tractors, a combine harvester, a dairy truck and large digger.
Simon Byrne, who runs a farm in Bunclody, Co Wexford said cutting essential payments to farmers would be dire as the money is the only stability they have.
"The weather this year was so bad so a lot of us really suffered during the harvest. The Government can't guarantee us good weather, but it can guarantee us our payments," said Mr Byrne.
Mary Mullane, who runs a family farm in Newcastle West, Co Limerick, said rocketing prices in diesel, grain, meal and silage have had a knock-on effect on farmers, meaning they need their subsidies more than ever.
"It's like a house of cards: if one thing goes, the rest can collapse," she said.
Mr Bryan, who met Agriculture Minister Simon Coveney, defended the right to demonstrate from criticism by small numbers of farmers on online forums and in contributions to radio programmes.
"Like all other working families, farmers have also had to find the money to pay significantly higher taxes and charges. Today farm families are saying, 'enough is enough'," he said.
Mr Coveney said he understands why the thousands of farmers are taking to the streets.
"There are major decisions being debated and made about the future of Europe for the next seven years," he said.
"We are at a crucial point now in the review of the common agricultural policy (CAP), which delivers €1.6 billion euro each year into Ireland currently."
Mr Coveney said Ireland would be central to the reforms, given that it will hold the European presidency in the first six months of next year.
Meanwhile, Fianna Fail spokesman for agriculture Eamon O Cuiv criticised the minister for his plans to impose cuts to a number of agricultural schemes, including the Agri-Environment Options Scheme, the Rural Environment Protection Scheme and the Disadvantaged Area Scheme.
"This sector is hugely important to the economy," said Mr O Cuiv.
"We need to ensure it is protected but all we have seen from this Government is stealth cuts and a total refusal to provide information in relation to the cuts."
The IFA is also stepping up pressure on Minister for Enterprise, Jobs and Innovation Richard Bruton to move immediately on government commitments to regulate retailers and restore equity in the food supply chain.