We know the closer in time between a protected activity and an adverse action, the more powerful is the inference the protected activity was a contributing factor to the adverse action. Indeed, where the protected act and the retaliation occur in quick succession, the inference is overwhelming.
But the opposite is true: the further the distance in time between the protected act and the retaliatory action, the weaker is the causal relationship.
A recent decision from the 2d Circuit Court of Appeals lists the seven types of circumstantial evidence that can be used to prove the protected activity was a contributing factor in the adverse action. Sirois v. Long Island R.R. Temporal proximity is one, and the Sirois Court considers when the gap in time is too wide to support a causal inference.
Here is the bottom line. If the gap is days or a few weeks? Very helpful compelling evidence. Several months? Not a problem, still a plus to stress. But a year or more? Now you are in territory where you need other contributory factor evidence to buttress the causal inference. And if the gap is two years or more, that is simply too attenuated to allow an inference of a causal connection.
However, there is an exception. In its Summary and Discussion of its Final Rules for the FRSA, OSHA pointed out that:
An employee can satisfy the contributing factor standard if he or she shows that the railroad’s adverse action took place within a temporal proximity of the protected activity, or at the first opportunity available to the retaliating manager, giving rise to the inference that it was a contributing factor in the adverse action. For example, years between the protected activity and the retaliatory actions did not defeat a finding of a causal connection where the manager did not have the opportunity to retaliate until he was given responsibility for making personnel decisions.
So if you can show a manager was just waiting for an opportunity to retaliate to arise, and then pounced when it did, a gap of years does not matter.