Social Security Clawback?

Hey guys I’m a Canadian doing some work for a US citizen and was wondering if one of you US guys could give me some help on a basic topic. If a US citizen is receiving a US pension, is there a clawback of social security benefits and if so, how do I calculate it? I seem to be finding one-off statements about clawback but I at a loss in terms of find any details about it. Thanks for the help! MLA