In the US, without net neutrality I believe it’s completely legal. I remember seeing a report on The Steven Colbert show about a year or so after we lost net neutrality about how Comcast deemed Netflix wasn’t paying them enough money so they throttled Netflix into the ground. This gave the appearance that Netflix services were crap in comparison to their own services like Hulu. About a month later they came to an agreement and Netflix paid up then magically speeds were restored to about the same as Hulu services.