Members pay the teamsters a flat rate per month not a percentage of what they make. The more employees the companies can hire, the more dues that the Teamsters get.
I witnessed a Teamster's Local allow their member's wages to be negotiated way down and the companies able to force old full-timers, that were at top-rate, out and replace them with a larger number of starting-rate employees.
The new contract made it very unattractive for new hirees to consider this line of work as a career, anymore.
The employers concentrated on hiring students that were looking to finance their education, so they could pursue other careers.
A very small percentage of these students ever stuck around long enough to make top-rate under the new contract.
The Teamsters collected more dues.
The Employers saved labor costs.
The union members got the royal shaft.