Comcast is firing warning shots over the FCC's historic decision Thursday.

The agency passed new Internet regulation prevent network owners -- like AT&T (T), Comcast (CMCSA), Time Warner Cable (TWC), and Verizon (VZ) -- from discriminating against what kind of traffic runs over their networks.

Comcast warned that a bitter legal fight is coming.

"After today, the only 'certainty'... is that we all face inevitable litigation and years of regulatory uncertainty," said Comcast's executive vice president, David Cohen.

It's similar to the warning AT&T's made earlier this month.

Comcast's legal threat is real, which is why despite the cheers of victory from populist groups on Thursday, the net neutrality fight is far from over.

The FCC rules won't be official until maybe summertime. That's when major telecom companies will challenge the rules in court.

A similar legal fight is why we're in this mess now. The last time the FCC tried to protect "Open Internet" rules, Verizon sued and the agency eventually lost in federal court.

Related: Telecoms say they aren't against net neutrality, they are against how the rules were changed

But Comcast also made a veiled threat to cancel plans to invest in its own broadband network.

"After seeing the Order, we'll have to engage in additional internal scrutiny on what our investment plans with respect to broadband will be going forward," Cohen at Comcast warned.

Telecom industry experts question this logic.

During Thursday's vote, FCC Chairman Tom Wheeler called the telecom industry's bluff over investment, saying that companies will continue to expand despite the new net neutrality rules.

Plus, if Comcast wants to merge with Time Warner Cable, a megadeal that's under review by the FCC, it will need to keep to its promise to invest in its network.

The whole purpose of the proposed merger "is to create the scale that will allow Comcast to make larger investments in R&D, innovation, and infrastructure to enable us to compete more effectively in this incredibly dynamic marketplace," Comcast promised in 2014.

Unless that marketplace suddenly has become uncompetitive, it still needs to invest. As does Time Warner Cable, Carter, Cablevision and the other large broadband Internet providers.