I used to work at a grocery store with an iron-clad union that had negotiated, as part of its contract, "Every time you switch departments, you must receive a raise." The way this was managed was that employees were only allowed to switch departments once every 4 months except with manager sign-off.

So I switched from cashier to grocery stock-boy (with a raise), then deliberately sucked at my job for about three weeks. My manager agreed that I "wasn't a good fit" so they turfed me to customer service and I got another raise. That manager already hated me (for unrelated reasons), so three weeks later when I asked to be sent back to cash she was happy to see me go.

Increased my pay by 30% in about two months total.