The laws of the state in which the employee performs work (i.e., is employed in) are what determines the rules for garnishment.
I disagree. In some circumstances the wages of an employee may be garnished by serving a garnishment order on the employer’s out-of-state office, e.g. headquarters or payroll processing office and the laws of the state where the garnishment was served would then apply. Maryland applies a rule that where the following two conditions are met the wages of an out-of-state employee may be garnished by serving the garnishment order in Maryland: (1) the case giving rise to that judgment against the employee was litigated in Maryland and the judgment entered in a court of Maryland and (2) the employer upon which the garnishment order is served is subject to the jurisdiction of Maryland courts, i.e. located in Maryland or has sufficient contacts in that state to be subject to jurisdiction there.
That rule comes about from a recent Maryland Court of Appeals case, in which the court states:
In conclusion, MCT could enforce the money judgments against Mr. Mensah through garnishments of Mr. Mensah's wages earned in Texas through the exercise of the original and ancillary jurisdiction of the district court that entered the judgments and because of BASF's business contacts in the State.
Mensah v. MCT Fed. Credit Union, 446 Md. 525, 542, 132 A.3d 332, 342 (2016). In that case, MCT had obtained a judgment against Mensah in Maryland District Court. It then obtained a writ of garnishment and served it on Mensah’s employer, BASF. At the time the garnishment was served, Mensah was a resident of Texas and worked for BASF in Texas. Mensah objected to the garnishment order saying that Texas law (much like Pennsylvania) bars wage garnishments for most private debts and that Maryland courts lacked the power to attach those wages. The court disagreed with Mensah and sided with the creditor in this instance, creating the rule I mentioned above.
Thus, if the OP is indeed sued in Maryland and the creditor obtains a judgment there, if his employer is subject to jurisdiction in Maryland by, say, having an office there, the judgment creditor could indeed garnish the OP’s wages in Maryland using Maryland’s wage garnishment rules, notwithstanding that Pennsylvania would not permit that same garnishment. The
Mensah case is just over 2 years old so it is very recent and has not been overturned.
Nor is Maryland unique in having this kind of rule. An attorney who practices in this area wrote an article for the site National Law Review which summarizes the rules in general for this sort of thing, but of course in any such case the law needs to be carefully researched as the states vary in the extent to which they follow the general principle mentioned in that article. You can find that article here:
https://www.natlawreview.com/article/compliance-rules-out-state-garnishments