More than 100 jobs could go at Diageo bottling plants in Glasgow and Fife, with plans by the drinks giant to move some packaging to Italy.
Seventy jobs are expected to go at Shieldhall by the end of the year and 35 at Leven, unless new bottling contracts can be won.
Diageo's bottling plant in Italy is running below capacity after it disposed of its wine business.
Unions at the main distiller of Scotch whisky strongly criticised the move.
Unite said it was a "shocking betrayal of Scottish workers" and the GMB said it was connected to the economic uncertainties arising from Brexit.
But Diageo said it followed a review of its spirits bottling business to ensure the company delivered "leading performance" in domestic and export supply chains.
Global supply chain
A spokesman added: "Regrettably, these changes may impact some roles in our European bottling plants towards the end of the year and we will now enter a period of consultation with our employees and their representatives to discuss the proposals in more detail.
"We are committed to our three spirits bottling sites in Europe - two in Scotland and one in Italy.
"The outcomes of this review will ensure we have the flexibility to respond to increased competition and external volatility, alongside testing and building the capability we need across our global supply chain to grow our brands."
There are currently 500 workers at Shieldhall, in south-west Glasgow, and 800 at Leven in Fife.
Cabinet Secretary for Finance Derek Mackay said Diageo's announcement was "deeply disappointing news".
He said: "Scottish Enterprise is engaging with the company to explore all possible options for supporting those affected, and we will work with the company to safeguard Scottish jobs.
"If any redundancies proceed, through our initiative for responding to redundancy situations, Partnership Action for Continuing Employment, we will provide skills development and employability support to minimise the time that individuals affected are out of work."