Unfortunately most do not understand how various departments within a company get unionized within a close shop union like the one at Enbridge.
Of course the Union would like more members, but they always balance that off with higher wages and benefits for their current members during negotiations on a new collective agreement.
While their is a litmus test use by Provincial governments on what jobs qualify for unionization in a company ( ie. are they supervisors with people under them or not as an example ). It usually boils down to the Union attempting to unionize a department or function within the company, then the company saying how bout we give you x% and certain benefits increases ( or at least holding the line ) in exchange for you dropping that issue. This all transpires at collective bargaining. It is treated as a monetary item and in the end the Union will always take more money for existing members over obtaining new members. If the Company does allow a department to Unionize it is most like because they don't really care, and that speaks volumes on how it perceives those workers. Believe me if they had a choice there would be no Union, so adding more members, as I have already stated means they don't really care. I know because I have sat on both sides of the table during collective bargaining within a closed shop union at Enbridge.