My employer is taking a portion of my earned tips

Location: Austin, Tx

I work at a restaurant as a server. It’s a small, family owned business open for 30+ years. When I started working for them, they did a quiz on me where I had to know everything on the menu and the exact ingredients for each. They said that if I passed, I got to keep more of the tips I earned. Before I took the test, I didn’t know, but I was only earning 50% of what I could have earned. For context, tips are pooled and split evenly based on the hours you worked that day. After the first test, I thought I passed and got all the tips I deserved. However,, after a few months of busting my as, I learned I was only earning 75% of tips.

I earn more than minimum wage, but I was always under the impression that employers could NEVER take tips earned by employees…

Is this legal???