Use it or lose it PTO Loophole? (CA)

My husband’s company PTO policy (based in California) is that they allow vacation days to carry over from the previous year until March at which point if you have any days left that is gone in April. I thought this was illegal under California wage laws but the way they do it makes me question if it is.

So for example, if you normally get 20 days PTO a year and carry over 5 days from 2025, January 1, 2026 the 2025 balance would be 5 days and 2026 balance would be 15 days. If you don’t use the 2025 balance by March, April 1 your 2025 balance goes away and 2026 becomes the full 20 days.

Is this legal? Is there somewhere my husband can file a complaint if it is not legal?