We filed our 1040 fed taxes and forgot to add union dues on line 21 schedule A for deductions.....do we need to do an amendment on 1040X.....?

It might not be worth the trouble..  Only the amount of job-related expenses that are OVER 2% of your adjusted gross income get added to your list of itemized deductions, which still must exceed your standard deduction in order to make a difference on your return.  This is kind of a hard deduction to get.  If you need to enter these, go to Federal>Deductions and Credits>Employment Expenses>Job-Related Expenses.