The chairman of the Federal Communications Commission suggested he might take legal action to block California’s net-neutrality bill, ratcheting up a high-profile clash over internet policy.  

California’s legislature passed its net-neutrality legislation in late August, after the FCC rolled back similar federal rules that had been adopted during the Obama administration. Net-neutrality rules generally prohibit internet providers such as cable and wireless firms from unfairly favoring some internet traffic over other traffic, such as by blocking or throttling websites and apps, or accepting payment to make them go faster.  

The Obama-era rules generally have been supported by big internet companies, which contend they help preserve online competition. Internet providers have fought them, arguing they represent a government overreach that could stifle innovation and investment. The internet providers say they will continue to abide by open-internet principles, even after the FCC rollback.

In response to the FCC’s rollback, a few states such as California have moved to impose their own versions of net neutrality. Gov. Jerry Brown hasn’t yet signed California’s bill, however, raising questions about whether he has doubts about it.  

FCC Chairman Ajit Pai, in a speech in Maine, warned that California’s net neutrality law would be “illegal,“ adding that ”we’re going to fight to make sure" that the FCC’s approach prevails.  

Mr. Pai says that state-by-state regulation of the internet would hurt consumers in other states.  

“California’s micromanagement poses a risk to the rest of the country,” Mr. Pai said. “After all, broadband is an interstate service; internet traffic doesn’t recognize state lines. It follows that only the federal government can set regulatory policy in this area.”  

He added that California’s strict law would be particularly painful for consumers, because of its bar on many types of free-data plans that favor some content over others. A typical example is when an internet service provider such as AT&T Inc. doesn’t count video it owns against its wireless customers’ data plans, giving them a strong incentive to favor AT&T content over competitors’.  

Such plans have proven popular, Mr. Pai contends, especially among lower-income consumers.