When Unwritten Law opens its tour with Sum 41 tonight (April 12) in Buffalo, N.Y., the group will be a little bit lighter. "Volatile circumstances involving disputes" between guitarist Rob Brewer and his bandmates, "as well as interaction between Brewer and the fans," led to his ouster last week from the rock act's ranks, according to a statement from Lava Records.

"It was an incredibly difficult decision, albeit the right thing to do given the recent circumstances," vocalist Scott Russo says. "Rob is irreplaceable and we plan to continue as a four-piece. We wish him the best and remain confident that Unwritten Law will continue to make great music."

Reports from a recent show at the House of Blues in Anaheim, Calif., describe Russo and Brewer verbally and physically fighting on stage.

This is the most recent of myriad lineup changes for the San Diego-based act, which last year saw lone remaining founding member/drummer Wade Youman replaced by Tony Palermo. The group is rounded out by bassist Pat Kim and guitarist Steve Morris.

Palermo was on hand for the recording of the band's fifth studio album, "Here's to the Mourning" (Lava), which bowed in February at No. 51 on The Billboard 200. The set has sold 88,000 copies in the United States, according to Nielsen SoundScan, and spawned the single "Save Me," which peaked at No. 5 on Billboard's Modern Rock Tracks chart.

Unwritten Law's tour with Sum 41 is scheduled into early June. Hawthorne Heights is on the bill for the tour's first half, while A Static Lullaby will take over in mid-May.