That's not really what happened here though. Congress long ago gave the FCC the authority to classify communications, establish rules for them, and enforce those rules...which is exactly what the FCC has been doing all along.
Congress didn't bat an eye when the FCC used their authority to (re-)classify cable, DSL, and wireless broadband in 2002, 2005, and 2007, respectively, under Title I of the Telecommunications Act, even though Title II had applied to some of those previously. After all, it was a burgeoning industry, so the lighter touch afforded by Title I made more sense, and there were other laws on the books to prevent the worst of the nasty things those companies might do.
Congress didn't bat an eye when the FCC used their authority to establish policy regarding net neutrality in 2005, establish ancillary regulations piecemeal over the years, or establish stronger protections for net neutrality in 2010. After all, as these companies were getting bigger, it was becoming more and more important to ensure that they acted in ways that were fair, and with the previous rules protecting against nasty things expiring, it was time to establish new ones.
Congress didn't bat an eye when the FCC used their authority to enforce fines against ISPs in response to nasty things they were doing. After all, them's the rules.
But then the Supreme Court slapped down one of the rules over a procedural issue, saying that if the FCC wanted to enforce that rule, they'd first need to reclassify those communications under Title II. The FCC attempted to work with the ISPs to come up with a middle-ground, but the ISPs refused to budge, so the FCC finally went and did exactly what the Supreme Court had suggested: they used their Congressionally-granted authority to reclassify those communications under Title II.
And now, suddenly, Congress is throwing a hissy fit. Why? Because, as it turns out, it isn't a burgeoning industry made up of companies like Prodigy and CompuServe still. Instead, it's made up of massive media and telecommunications conglomerates like Comcast, AT&T, and Verizon with hundreds of billions of dollars on the line, and they are not happy with having an appropriate classification applied to them, given that it's a lot more fun to be a misbehaving behemoth.
The text of the rules has been public for months, even though it hadn't been added to the Federal Register yet. This isn't a "we have to pass it to see it" situation at all. And Congress has no good reason for sticking their noses into this situation, unless you consider the millions and millions of dollars they're receiving to be a good reason.