The Burford abstention, first enunciated by the Supreme Court in Burford v. Sun Oil Co., 319 U.S. 315, 63 S.Ct. 1098, 87 L.Ed. 1424 (1943), just two years after Pullman, held that federal courts should exercise equitable discretion and refrain from exercising authority over questions involving basic problems of state policy pertaining to the regulation of important state natural resources, even if federal court jurisdiction is predicated on diversity of citizenship. The Court subsequently observed in Colorado River Water Conservation District v. United States, 424 U.S. 800, 96 S.Ct. 1236, 47 L.Ed.2d 483 (1975): Where the State had established its own elaborate review system for dealing with the geological complexities of oil and gas fields, federal review would have had an impermissibly disruptive effect on state policy for the management of those fields. Id. at 815, 96 S.Ct. at 1245. Burford abstention is usually applied to state regulatory matters such as establishing rates for natural gas or transportation, discontinuing railroad passenger services, Alabama Public Services Commission v. Southern Railway, 341 U.S. 341, 71 S.Ct. 762, 95 L.Ed. 1002 (1951), discontinuing intrastate air service, Allegheny Airlines v. Pennsylvania Pub. Util. Com'n, 465 F.2d 237 (3d Cir.), cert. denied 410 U.S. 943, 93 S.Ct. 1367, 35 L.Ed.2d 609 (1973), or applying state eminent domain procedures, Ahrensfeld v. Stephens, 528 F.2d 193 (7th Cir.1975). In Burford v. Sun Oil, the Supreme Court explicitly premised its order of abstention on the power, unique to courts of equity, to refuse, for policy reasons, to exercise their jurisdiction: Although a federal equity court does have jurisdiction of a particular proceeding, it may, in its sound discretion ... refuse to enforce or protect legal rights, the exercise of which may be prejudicial to the public interest....(319 U.S. at 317-18, 63 S.Ct. at 1099.) Burford abstention is not the only abstention doctrine grounded in the unique power of courts of equity. Cases involving other abstention doctrines also emphasized that the source of the courts' authority to develop a doctrine of abstention was based upon the discretion to decline or grant equitable relief. See Baggett v. Bullitt, 377 U.S. 360, 375, 84 S.Ct. 1316, 1324-25, 12 L.Ed.2d 377 (1964); Younger v. Harris, 401 U.S. 37, 91 S.Ct. 746, 27 L.Ed.2d 669 (1971); Railroad Comm'n of Texas v. Pullman Co., 312 U.S. 496, 500-01, 61 S.Ct. 643, 645-46, 85 L.Ed. 971 (1941). The reasoning of Burford, Pullman and the other cases locating the power to abstain in the unique powers of equitable courts has never been rejected. The Supreme Court has, however, subsequently applied some forms of abstention doctrine to cases at law, without discussion. Furthermore, the Supreme Court explicitly expanded some forms of abstention to a few "special" classes of damage actions. These cases were severely criticized by dissenting justices. In his dissent in Fair Assessment in Real Estate Association v. McNary, Justice Brennan pointed out that "[w]hile the 'principle of comity' may be a source of judicial policy, it is emphatically no source of judicial power to renounce jurisdiction.... There is little room for the 'principle of comity' in actions at law where, apart from matters of administration, judicial discretion is at a minimum." 454 U.S. 100, 119-21, 102 S.Ct. 177, 188, 70 L.Ed.2d 271 (1981) (Brennan, J., dissenting).