Merriam-Webster’s Dictionary defines “cat’s paw” as “one used by another as a tool.”  In the legal sense, “cat’s paw liability” refers to the situation in which an employer is held liable for discrimination when it relies on a supervisor’s biased report and takes an adverse employment action against an employee.
The United States Supreme court affirmed this theory of liability in Staub v. Proctor Hospital, No. 09-400, 562 U.S. (2011), holding that “if a supervisor performs an act motivated by antimilitary animus that is intended by the supervisor to cause an adverse employment action, and if that act is a proximate cause of the ultimate employment action, then the employer is liable” under the Uniformed Services Employment and Reemployment Rights Act of 1994 (“USERRA”). 
The plaintiff in the case, Vincent Staub, worked as an angiography technician for defendant Proctor Hospital until 2004, when he was terminated.  While employed by Proctor, Staub was a member of the United States Army Reserve, which required him to attend drill one weekend per month and to train full time for two to three weeks a year.  Both Janice Mulally, Staub’s immediate supervisor, and Michael Korenchuk, Mulally’s supervisor, were hostile to Staub’s military obligations.  In January 2004, Mulally issued Staub a “Corrective Action” disciplinary warning without justification.  Then in April 2004, Korenchuk informed Proctor’s Vice President of Human Resources, Linda Buck, that Staub had violated the Corrective Action, which again was false.  Buck relied on Korenchuk’s accusation and fired Staub.
Staub sued Proctor under USERRA, claiming that his discharge was motivated by hostility to his obligations as a military reservist.  He did not contend that Buck had any such hostility, but instead that Mulally and Korenchuk did, and that their actions influenced Buck’s ultimate decision.
Proctor argued that an employer cannot be held liable for discrimination unless the ultimate decisionmaker is motivated by discriminatory animus.  The Court rejected this argument and reasoned that so long as the earlier agent or supervisor intended, for discriminatory reasons, that the adverse action occur, the wrongful intent required for liability exists.