Normally, after a case is removed to federal court, a decision of the district court to remand the case back to the state court is not reviewable on appeal. However, under 28 U.S.C. sec. 1447(d), appellate review is available where the case for removal is based on the involvement of a federal officer (sec. 1442) or concerns civil rights (sec. 1443). When Baltimore’s mayor and city council sued certain energy companies for allegedly concealing the environmental impact of their products, those companies removed the case to federal court in part based on sec. 1442. The district court ordered the case to be sent back to the state court, and the Fourth Circuit read sec. 1447(d) as only allowing review of jurisdiction under sec. 1442, and not the other bases offered by the companies.
The Court, in a 7-1 opinion by Justice Gorsuch (Justice Alito recused), reversed, ordering that the circuit courts are allowed to review the entire remand order so long as sec. 1442 or 1443 is part of the request for removal. The Court noted that Congress did not require that appellate review be limited “solely” to the approved grounds of removal, and thus it was inappropriate to so limit it here. Justice Sotomayor’s dissent argued that the majority’s decision “lets the exception swallow the rule.”
A link to the decision in BP PLC v. Mayor and City Council of Baltimore is here: https://www.supremecourt.gov/opinions/20pdf/19-1189_p86b.pdf