28 U.S.C. § 1447(d) provides that "[a]n order remanding a case to the State court from which it was removed is not reviewable on appeal or otherwise." Under Thermatron Prods., Inc. v. Hermansdorfer, 423 U.S. 336 (1976), the jurisdictional bar of § 1447(d) is limited to the grounds enumerated in § 1447(c). The question of first impression in HIF Bio, Inc. v. Yung Shin Pharms. Indus. Co., 2007 U.S. App. LEXIS 26329 (Fed. Cir. Nov. 13, 2007), was whether appellate review of a remand order declining to entertain supplemental jurisdiction under § 1367(c) was barred. The Federal Circuit teed up the issue as follows:

If the district court had not had supplemental jurisdiction over the state claims, the remand would have been based on a lack of federal question or diversity jurisdiction. In such case, deciding whether § 1447(d) bars review would be straightforward. A remand for lack of federal question or diversity jurisdiction is clearly a remand for lack of subject matter jurisdiction under § 1447(c) and thus barred from appellate review by 1447(d). [Citation omitted.] However, in this case, because the remand order was based on declining supplemental jurisdiction pursuant to § 1367(c), we are faced with an issue of first impression for this court: whether a remand based on declining supplemental jurisdiction under § 1367(c) is within the class of remands described in § 1447(c), and thus barred from appellate review by § 1447(d).

Concluding that the answer was affirmative, and that appellate review was foreclosed, the Federal Circuit reasoned that:

In short, because every § 1367(c) remand necessarily involves a predicate finding that the claims at issue lack an independent basis of subject matter jurisdiction, a remand based on declining supplemental jurisdiction can be colorably characterized as a remand based on lack of subject matter jurisdiction. Accordingly, a remand based on declining supplemental jurisdiction must be considered within the class of remands described in § 1447(c) and thus barred from appellate review by § 1447(d).