Taking a price fixing class action to trial is not for the faint of heart. Damages are trebled, and any defendant left standing could be on the hook for the whole shebang.

That specter seemed to loom large for International Paper, which on Wednesday announced it would pay $354 million to settle a suit alleging seven industry players conspired to fix the price of containerboard products like corrugated boxes—a market that while unglamorous, is absolutely enormous.