The three - two based in Fife and one from East Dunbartonshire - all scooped £1 million in the EuroMillions Millionaire Raffle draws in July.
But they have not yet come forward to collect their winnings and the 180-day period in which they can do so has almost expired.
National Lottery bosses are urging EuroMillions players in those areas to look for their old ticketss.
For every EuroMillions line played, UK players automatically receive a EuroMillions Millionaire Raffle selection printed on their ticket.
Two of the winning tickets, one from Fife and one from East Dunbartonshire, are from the draw on July 26.
The raffle numbers are CZZ474287 and CBT475280.
Their deadline is 11pm on Wednesday January 22.
The other Fife winner netted £1m on July 23 with the raffle number BZP849967. They only have until 11pm on Sunday, January 19 .
If no-one comes forward, all the money will go to the National Lottery Good Causes fund.
Meanwhile, John Hay, 38, from Billingham, and his mother Doreen, 70, from Thornaby, both Teesside, who scooped £7.5m on the National Lottery only found they had won on Sunday morning when she checked the newspapers.