Scottish beef could become scarce in the UK as increasing amounts are exported to Ireland and Italy, according to NFU Scotland.
Good export prices for quality Scottish beef meant more animals were being sent abroad, NFUS said.
While this was good for producers in the short term, it could destabilise the industry in the long term if retailers found it difficult to source meat in the home market, the union added.
A weaker sterling has led to more European buyers sourcing from Scotland, said NFU Scotland livestock committee chairman Kelvin Pate. This meant UK supermarkets needed to incentivise producers to sell to the domestic market, he added.
"This is a potential time bomb for the Scotch Beef brand and rings alarm bells about future supply," he said. "Animals from the top end of the market are being exported in huge numbers."
If top-quality Scottish meat continued to be exported, this would probably be replaced on shelves with "inferior imports", Pate added.