In Stout v. City of Wagoner, a 2008 Oklahoma federal court case, a former police officer sued his department when he was fired 10 years AFTER he ran an political ad against the police chief. During the 10 year period, the officer had been offered several promotions and had eventually accepted a promotion to lieutenant. The Court, in dismissing Stout's claims, held that lapses in time between conduct and termination establish that retaliation was not a reason for termination as anger and resentment are emotions that diminish with time.
In a Connecticut federal court case decided around the same time, a district court judge ruled that no reasonable member of a jury could find retaliation when five years had elapsed between the former employees actions and ultimate termination. See Giglio v. Derman, 560 F.Supp.2d 163 (D.Conn. 2008).
There is no bright line rule about how long is too long for retaliation claims, but more and more cases are showing that the more time that does elapse between protected activity and adverse action, the less likely an employee can bring a successful retaliation case. For more information, see the October 2008 Public Safety Labor News.