If union dues are reported on my W2, do I also note them in the deductions section?

Yes, you can, if you Itemize your deductions.

If your Union Dues are on your W-2 in Box, TurboTax will automatically enter the union dues on Schedule A, Itemized Deductions, Line 21, Unreimbursed employee expenses.

Unreimbursed employee expenses are subject to the 2% rule. Click on What is the 2% rule?

For additional information on where to enter Unions dues if you are self-employed or they are not reflected on your W-2, click on Can I deduct union dues, and where do I enter them in TurboTax?