General Meaning (Karma/Retribution):
* You reap what you sow
* What you give is what you get
* As you make your bed, so you must lie in it
* Justice will prevail
* The chickens will come home to roost
* Payback is a b (not appropriate for all contexts)
* Karma's a b (not appropriate for all contexts)
More Specific Meaning (Consequences):
* Actions have consequences
* Every action has a reaction
* You get what you deserve
* The tables will turn
* It's a boomerang effect
* The law of unintended consequences
Figurative Expressions:
* The wheel of fortune turns
* What goes up must come down (literal meaning also applies)
The best synonym to use depends on the specific context and the intended tone.