From what I have read, you may not be able to deduct.  To verify, I would suggest you contact Maryland.  Click here: https://ttlc.intuit.com/community/state-taxes/help/how-do-i-contact-my-state-department-of-revenue/0...

Also, see instructions for the form, https://www.marylandtaxes.gov/forms/19_forms/resident_booklet.pdf

@riv1215

Contacted the comptroller of Maryland and they said no.  

As of Tax Year 2023,  Maryland state employees can deduct union dues on stat. From my understanding, the cap is $250. Is this correct? And where would I include it on my state return?

Information flows from the federal return to the state return.  Although your union dues are not deductible on your federal return, you enter them while you are working on your federal return.

-W-2 employees cannot deduct job-related expenses on a federal return.  Job-related expenses were eliminated as a federal deduction for W-2 employees by the tax laws that changed for 2018 and beyond.  Your state tax laws might be different in AL, AR, CA, HI, MN, NY or PA.

If you live in a state that lets you deduct job-related expenses, the information will flow from your federal return  to the state return, so enter it in Federal>Deductions and Credits>Employment Expenses>Job-Related Expenses