The SCO Group has upped the ante in its $3bn lawsuit battle with Big Blue by terminating IBM-owned Sequent's Unix licence, claiming it supplied much of the disputed lines of code in Linux.

According to SCO, IBM-Sequent was given two months written notice prior to the termination of Dynix/ptx, as required by the contract, and licences granted to customers will be considered invalid.

SCO claims that around 168,276 lines of code and 148 files came from Sequent's Dynix/ptx Unix, and were used in the Linux 2.4 and 2.5 kernels.

The action follows SCO's termination of IBM's AIX Unix licence in June, and is believed to reflect its bitterness over the aborted Project Monterey.

IBM bought Sequent Computer Systems in July 1999 for $800m. At the time IBM, Intel and SCO were involved in Project Monterey, which set out to develop a new Intel-based Unix operating system.

The project combined technology from IBM's AIX and SCO's UnixWare, as well as using Sequent's non-uniform memory access (Numa) technology, which became the property of IBM.

"This Sequent code is critical Numa and read-copy-update multi-processor code previously lacking in Linux," said SCO in a statement.

In a recent interview with vnunet.com, SCO chief executive Darl McBride said: "When IBM walked away from Project Monterey it put a dagger into the heart of SCO. Santa Cruz Operation lost its heart at that point and sold ts business to Caldera."

There is no dispute that Numa technology, originally developed by Sequent, has been added to Linux. But SCO contends that, as it is the licence holder for Unix System V, companies cannot contribute their Unix code to Linux without its permission.

"Sequent-IBM failed to treat Dynix as part of the original System V software and exceeded the scope of permitted use under its Unix System V contract with SCO," said the company's statement.

IBM was not available for comment.