The Aboriginal owners of two clothing businesses are shocked after receiving legal letters demanding they stop using the Aboriginal flag on their merchandise because it "violates Australian copyright laws".

The NRL, Cricket Australia and the AFL may also have been issued notices by Queensland-based WAM Clothing over the use of the Aboriginal flag on clothing, The Age and The Sydney Morning Herald understand.

Gunditjmara Woman Laura Thompson, the managing director of Spark Health Australia and Clothing The Gap. Credit:Luis Ascui

Clothing the Gap is a small "profit for purpose" business based in Preston, in Melbourne's north, which produces clothing and accessories that feature the Aboriginal flag, including contemporary T-shirts and towels.

Co-owner, managing director and Gunditjmara woman Laura Thompson says she was shocked to receive the legal letter.