It's not "even when not itemizing." The deduction is only available if you itemize deductions on your New York tax return (whether or not you itemize on your federal return). The UUP article that you referenced says "Legislation passed in 2017—as part of the state’s 2018 Enacted Budget—created a union dues deduction for New York union members who itemize deductions on their state tax returns" [italics added]. The governor's press release that the UUP article references says "The FY 2018 Enacted Budget creates a union dues deduction for New York taxpayers who itemize deductions at the state level . . ." [italics added].
On the plus side, it's for anyone who pays union dues, not just teachers.
If you are using the CD/Download TurboTax software you can enter the deduction in forms mode. Open the Other Additions Adjustment Statement for Form IT-196. Enter the union dues on line 4 (item K) of the Adjustment Statement. It will flow to Form IT-196 line 44. I don't see any way to enter the deduction in the New York interview, which means you cannot enter it in TurboTax Online. I will point out the omission to the community moderators. I doubt that TurboTax will add it to the interview this year, but maybe next year.
