NFU Scotland said producers were losing about Â£10 for every pig that is sold.
Prices have been driven down from a record high in 2013 after a Russian import ban led to an oversupply of the meat in Europe.
Farming leaders now plan to meet retailers to discuss the promotion of Scottish pork over cheaper rivals.
Midlothian pig farmer Robin Traquair said the dramatic price drop could lead to some producers going out of business.
"Farmers are losing money, they are in a cash negative situation, their bank balances are going backwards," he said.
"Investment won't be done, they won't become more efficient, people will start to go out of business."
At its peak, he said he received Â£120 for each pig he produced. Now he sells them for about Â£85.
"We sell 10,000 pigs a year so it's a big lump of cash," he said.
"Now the commodity prices, the cereal prices have come down but it's not come down far enough to cover that."
Mr Traquair, who owns Wellington Farm, said he was unable to invest in sheds or equipment which would make the business more efficient.
He said their choice was either to "pack in or knuckle down".
"At the moment there's some things we should do with spending money on - but we're just going to batten down the hatches and ride it out. It's tough," he added.
NFU Scotland said that a new processing plant is now operating in Brechin, which could halt the price decline.
It plans to meet retailers to discuss "positioning and publicity" of Specially Selected Pork, which guarantees high welfare standards as part of Quality Meat Scotland.
Kevin Gilbert, NFU Scotland's pigs committee chairman said pig prices had fallen by 18% in the last year.
"Production simply cannot be sustainable at these prices," he added.
"It is clear that a lot of cheaper European meat is being substituted for UK product, especially in processed meat products.
"Retailers could really help UK producers at this time by showing greater loyalty to Scottish and UK product.
"This should be a time of positivity for the Scottish pig industry as the new abattoir at Brechin is set to double its processing capacity, allowing more Scottish pigs to be processed in Scotland, which will reduce haulage costs and allow wider stocking of Scottish labelled Specially Selected Pork across the major supermarkets in Scotland."
Scottish pig farmers have warned they are facing an uncertain future after the price of pig meat hit an eight- year low.