Aegis's basically answered it above but - in classical special relativity, as understood to this undergrad-but-physics-major, if you accelerate yourself to ten nines of c and then instantaneously travel backwards some distance in your reference frame (pretty sure it needs to be big, like light-years big), instantaneously stop yourself and then teleport back to your original position, you'll have moved backwards in time. This is likely to be done accidentally if, say, you have this arrangement of colonies (roughly)

A------B-----C

and someone departs B going to C, but sends a message by ansible to A that gets rebounded to B.

Which, depending on how fast the ship was moving and how far the colonies are, might never be noticed by the colonists themselves. It should be blindingly obvious to you, though - my naive model of relativity says that every time someone gets up to relativistic speed then some part of your consciousness ends up behind some part it used to be ahead of, so if you haven't noticed anything my naive model of relativity is hilariously wrong.

Which is good! Means I'll still have a job when I finish my PhD. :P