The retailer opened two big stores in Edinburgh and Glasgow last year. According to the union, Debenhams intends to continue this practice, and will open in Dundee, East Kilbride and Inverness.
The event will also be used to raise awareness for an initiative to introduce a Scottish Parliament Bill banning large-format stores from trading on Christmas holiday dates.
MSP for Airdrie and Shotts Karen Whitefield is spearheading the campaign. She said: 'I firmly believe that we in Scotland should protect the special nature of these public holidays. I also believe that shopworkers who work tirelessly throughout the year deserve the right to spend these two important days at home with their family.'