You can deduct your union dues each year as a miscellaneous deduction. Unfortunately, you are not permitted to add prior years' dues on your 2016 return. You can only deduct the 2016 dues on your 2016 return. You can, however, amend your tax returns for the prior three years and add on the deduction. Depending on the amount of dues you pay and your annual income, it may not be worth the effort to amend.