SCO has not decided how much it will charge users, and it is still examining the licence structure.
Darl McBride, SCO's chief executive and president, said the company has "broad enforcement capabilities" regarding copyright of software containing Linux kernel 2.4 or above, which is commonly used in businesses around the world.
Rakesh Kumar, an analyst with Meta Group, called SCO's move "amateurish" and said it would be difficult to prove infringement of copyright in this instance. "It seems like a panicked approach to try to get revenue," he said.
Michael Bywell, a partner in the technology, media and communications group at international law firm DLA, said Linux users faced with such an approach by SCO should conduct legal due diligence to work out whether they are vulnerable to legal claims. They should also ask SCO to show in clear terms exactly where its copyrights have been infringed.
SCO's announcement sees the company widen its ongoing, $3bn (£1.9bn) contract violation case against IBM, which it claimed damaged demand for Unix by releasing elements of its System V Unix code into the open source community. SCO terminated IBM's Unix licence last month.
A legal representative for SCO, David Boies of Boies, Schiller & Flexner LLP, said the company did not need to resolve the IBM case before it starts taking court action against Linux users.