The closures over the next 12 months could see more than 330 jobs potentially lost.
The affected stores are Bournemouth, Stockton, The Fort, Shipley, Scunthorpe, Narborough Road, Grantham, Redditch, Rotherham, Skegness, Sutton, Coldfield, Orpington, Edmonton Green, Llanelli, Merthyr Tydfil and Cleethorpes.
The Rotherham branch, which has 20 members of staff, is set to close on June 4.
“It’s yet another nail in the high street’s coffin and GMB calls on councils and landlords to review commercial leases and offer lower rents.
“Empty high streets and shopping centres are in no one’s interest and but with 400 shops a week closing, this is inevitable - unless the costs of premises can be reduced.”