The plaintiff who seeks to maintain an action in tort against a federal employee has basically two choices. First, after complying with various procedural requirements, the plaintiff may initiate suit under the Federal Tort Claims Act (FTCA) against the United States. The act is a waiver of sovereign immunity and, in spite of the existence of exceptions to its coverage, has generally been interpreted broadly.
The other alternative available to the plaintiff is a suit against the employee in his individual capacity based upon either state-law or constitutional tort. One of the employee's first lines of defense against such actions is official immunity. Fairly distinct bodies of law have developed for immunity in suits alleging constitutional torts and those based in state-law. Courts generally recognize absolute immunity from tort actions for executive officials in quasi-judicial functions.
A federal employee sued in state-law tort will seek the protection of absolute immunity. The leading Supreme Court case in the area is Barr v. Matteo. The case had come to stand for the rule that a federal employee was entitled to absolute immunity against suit based in state-law tort when the actions giving rise to the suit were ‘within the outer perimeter of the employee's line of duty.’ The courts of appeals split on whether immunity also required conduct that was ‘discretionary’ in nature. The Supreme Court resolved this conflict in Westfall v. Erwin, by unanimously holding that discretion was indeed a prerequisite to absolute immunity. In spite of the Court's efforts to provide some guidance for a workable definition of ‘discretion,’ the case raises serious concerns over how federal officials should function and when they can be held individually responsible for damages resulting from the performance of their duties.
Karl R. Rábago, Absolute Immunity for State-Law Torts Under Westfall v. Erwin: How Much Discretion Is Enough?, Army Law., Nov. 1988, at 5, http://digitalcommons.pace.edu/lawfaculty/946/.