Unless your client telecommutes from GA for the convenience of the NY employer, compensation is sourced to NY based on NY statutes regardless of how the taxpayer's resident state may source that income.  This creates a potential exposure to double taxation as states typically look to their own sourcing rules for purposes of other state credit.  NY's position had been challenged in courts but prevailed.

As telecommuting became more common as a result of COVID-19, MA joined NY in instituting a similar tax policy to tax telecommuters who would otherwise physically work in MA.  MA argues that the new rules are meant to maintain the status quo but these have drawn the ire of NH which petitioned the US Supreme Court to hear the case.  CT (which implemented a reverse telecommuter tax recently) and NJ have since joined MA in the petition.  If the Supreme Court takes up the case, the outcome may affect NY's tax rules on telecommuters.

The exposure of telecommuters to double taxation is not new.  Bills were introduced in 2004 and 2016 by Congress to address these issues but these didn't get anywhere in the end.

It's one of those situations where a client could have talked to us in advance before the arrangement is materialized and we have no good news to deliver if we come to know about it only after the fact.