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."

Alexander Wotherspoon, 83, appeared at Paisley Sheriff Court charged with causing the death of Eilish Herron by driving without due care and attention.
The 17-year-old was struck by Mr Wotherspoon's car at an Asda petrol station in Linwood in September 2014.
The charge says he had failed to keep control of the car while reversing.
Mr Wotherspoon, from Houston in Renfrewshire, uses a zimmer frame to help him walk.
He denied starting the engine of his car and reversing while the driver's door was still open, failing to keep control of the car and, while it was reversing, causing it to hit the Renault Clio Eilish was filling up with petrol.
The charge states that his actions knocked her to the ground, moved her car out of the way and caused his car to reverse over her, dragging her underneath the car, "causing her to be so severely injured that she died."
The incident happened at the Asda petrol station at the Phoenix Retail Park in Linwood on 10 September 2014.
Sheriff Susan Sinclair adjourned the case for a trial to take place in August and continued Wotherspoon's bail.
Speaking previously, Eilish's mother Shanneal, 47, said: "Eilish was a really good girl, a normal teenager who loved her life, loved her family and loved her sport.
"She was my best friend, we had such a good laugh.
"I can't put into words how much she's missed in our family. We are all very close."
Eilish was a keen netball player and played for Paisley Juniors as well as volunteering as a junior coach.
After her death, Netball Scotland created the The Eilish Herron Young Coach of the Year Award, which will continue as a yearly recognition award for young coaches.
Scottish pig farmers have warned they are facing an uncertain future after the price of pig meat hit an eight- year low.
[NEXT_CONCEPT]
A pensioner has denied causing the death of a teenage girl by by reversing over her as she was filling her car up with petrol in Renfrewshire.