The operators of the Hetland Hall Hotel near Dumfries want to add bedrooms, an events space and lodges.
The action will mark the first ever hospitality strike in the North West, according to the union.
The review of how rates are calculated in England and Wales could lead to reform of the system.
There is concern about the possibility of Chateau La Chaire hotel becoming a residential property.
Jo Boydell had faced criticism after the sexual assault at the Maidenhead hotel was reported.
The new owners say the business will be an important part of the town's regeneration.
Jo tells the BBC about the "terrifying" moment when she saw a man's silhouette by her hotel bed.
The owners of Chateau La Chaire say the change will "secure the long-term future" of the building.
A woman tells the BBC her attacker kicked her hotel room door "off its hinges" after reception gave him the key.
