https://www.cnet.com/news/california-net-neutrality-law-sparks-justice-department-lawsuit/

Interconnection happens when two network operators hand off traffic to one another. For example, when Netflix delivers video streams directly to broadband providers, like Verizon and Comcast, which control the internet connection into people's homes. Companies negotiate private contracts over those handoffs. And California's law ensures the rules of no-blocking, no-throttling and no-paid prioritization also applies when traffic is being handed off.

California's net neutrality efforts have long been opposed by the Trump administration, which late Sunday announced its intention to file a lawsuit to block the law. US Attorney General Jeff Sessions said California's new legislation places an unlawful burden on the US government's efforts to deregulate the internet.