Unite union claims the owner of the specialty Johnston Street boutique has refused to remunerate Emily Gray and Bree Wilson a total of $8000 for work performed last year.

However, in an email sent to Unite, the owner claims both women were knowingly offered only voluntary positions to give them retail and networking skills.

Emily Gray said she worked at the store for three to four hours a week over seven months last year. She said she was owed about $2000.

"She [the owner] needed help in the shop and she said I can't pay you at the moment, but once the shop's doing all right, that will happen, but that never happened," Ms Gray said. "So that's when I decided to leave."

MTW contacted the store owner for comment, but she did not respond before deadline. Ms Wilson could not be contacted for comment.

Unite organiser Chris Dite said the owner refused to pay the women when approached late last year.

"It is absolutely ludicrous that [she] thinks that people should work for free. We are demanding that she pay our members the money they are owed."

Mr Dite said the union may organise a protest outside the Johnston Street store and take the matter to Fair Work Australia.