Had a (roughly) similar experience when I used to work for a construction company. Once, a job was behind schedule, and they asked us to voluntarily work on a Saturday. Virtually everyone did, because working on a weekend got you time and a half pay.
Instead of a full day, though, they sent us home at lunchtime. Nobody was expecting that. One guy summed it up pretty well: “I got up at 6 AM on a Saturday to make less than I did yesterday? This is bullshit!”
After that, whenever our bosses asked if we’d come in on a Saturday, someone asked if it would be a full day or a half day. When our bosses said “I don’t know” (which is what they said every time) nobody came in.
They got away with exploiting us once, but completely screwed themselves in the long term. I was (and still am) very proud of my coworkers for continuing to hold management accountable for their decisions.