The deduction for union dues is in the same section of the Income Tax Act as professional fees. I am a lawyer. I have to pay my bar fees, or I cannot work. I am also a steamfitter. I can be a union steamfitter or a non-union steamfitter. It's my choice.
If the unions have to disclose, why don't the professional associations, which must get exactly the same tax-funded status as the unions, have to disclose? Why wouldn't an employer's association, which has exactly the same funding structure and the same tax break, not have to disclose?