At issue is "Net neutrality" – the principle, as Andrew LaVallee of the Journal puts it, that "all Internet providers should treat all data equally and avoid restricting or delaying access to certain sites." Over the past few years, many large ISPs, including Comcast, have pushed back against previous FCC efforts to enforce net neutrality.
The reasoning: Users with slow connections can jam up the Internet for everyone else. Plus, Comcast owns the company, so Comcast should be able to make the rules. But public interest groups have argued that consumers would benefit from a law enforcing Net neutrality.