The escalating skirmish between the two companies began when Oracle purchased computer producer Sun Microsystems, The (San Jose, Calif.) Mercury News reported Thursday.
That purchase made longtime collaborators into competitors.
Last year, when HP fired executive Mark Hurd after a relationship scandal involving an HP contractor, Oracle Chief Executive Officer Larry Ellison reached out and hired Hurd, who he considers a friend.
That provoked a lawsuit as HP contended Hurd would divulge company secrets at his new job.
The suit was later dropped when Hurd gave up his HP stock.
HP now claims Oracle has libeled the company and left 140,000 of its high-end customers high and dry when it decided to stop producing software for computers running Intel's Itanium processor that HP sells for $200,000.
In a statement, Oracle said HP's executives "know full well" that Intel was phasing out the Itanium chip.