They could be asking for tax purposes. I have a business number and i have only ever given it to one family. Actually, the family asked me for my SIN originally so they could do their taxes and i told them i don't give it out, just my B#. They claim their accountant needed it to do their taxes, so i told them that my accountant told me only to ever give out my B# for business purposes and they can contact each other for clarification. Family said ok and took my B# and i never heard about it again.