312 U.S. 496 (1941)
In those sections of Texas where the local passenger traffic is slight, trains carry but one sleeping car.1 Unlike trains having two or more sleepers, these trains are without a Pullman conductor; the sleeper is in charge of a porter who is subject to the train conductor’s control.2 As is well known, porters on Pullmans are colored and conductors are white.3 Addressing itself to this situation, the Texas Railroad Commission, after due hearing, ordered that no sleeping car shall be operated on any line of railroad in the State of Texas unless such cars are continuously in the charge of an employee having the rank and position of Pullman conductor.4
The Pullman Company and the railroads affected brought this action in a federal district court to enjoin the Commission’s order.5 Pullman porters were permitted to intervene as complainants, and Pullman conductors entered the litigation in support of the order.6 After three judges were convened pursuant to Judicial Code § 266, as amended, 28 U.S.C. § 380, the court enjoined enforcement of the order, and from this decree the case came here directly under Judicial Code § 238, as amended, 28 U.S.C. § 345.7
The Commission found justification for its order in a Texas statute, Vernon’s Anno. Texas Civil Statutes, Article 6445.8 Article 6453 of the Texas Civil Statutes gives a review of such an order in the state courts, and Article 6476 provides an alternative method for the State to enforce obedience to the order.9
Whether the federal district court should have exercised its equity jurisdiction to adjudicate the challenges to the Texas Railroad Commission's order or instead stayed its hand pending a definitive ruling by Texas state courts on the scope of the Commission's authority under state law?10
Federal courts exercising equity jurisdiction must restrain their authority out of scrupulous regard for the rightful independence of state governments.11 This restraint is required when a case presents an unsettled question of state law whose resolution by state courts could avoid constitutional adjudication and prevent needless friction with state policies.12
No. The district court should not have exercised its equity jurisdiction to adjudicate the challenges to the order.13 Instead it should have stayed its hand pending a definitive state-court ruling.14 The Texas Railroad Commission justified its order under Article 6445 of the Texas Civil Statutes by invoking the statutory mandate to prevent unjust discrimination and all other abuses in railroad operations.15 Whether that authority reaches the staffing arrangements for single sleeping cars operated by porters rather than conductors is far from clear under Texas law.16 The district court's denial that the statutes sustained the order amounted only to a forecast rather than a definitive determination.17 The Supreme Court of Texas possesses the final authority to interpret Article 6445.18
Proceeding to enjoin the order on that tentative basis would risk an unnecessary federal ruling supplanted by a controlling state adjudication.19 This would undermine the policy of avoiding premature constitutional decisions and promoting harmonious state-federal relations through the resources of equity.20
The cause must be remanded to the district court with directions to retain the bill pending a determination of proceedings to be brought with reasonable promptness in the state courts.21