The patentee must demonstrate that the injunction it seeks should issue. Generally, Federal Circuit precedent has held that an accused infringer may successfully challenge a motion for preliminary injunction by raising a "substantial question" concerning validity, enforceability or infringement.
But a recent Federal Circuit opinion, Abbott Labs. v. Sandoz Inc., 544 F.3d 1341 (Fed. Circ. 2008), calls that standard into question and heightens the defendant's burden for successfully challenging the likelihood of success on the merits factor. Read more.