Fossil fuel producers and power plant operators.

A few states, and therefore a motivated group of Senators, would be hit disproportionately hard. Places like Wyoming and West Virginia drive a considerable part of their economy from coal, and fracking has led to natural gas windfalls in states like North Dakota.

You would imagine that some large carbon-intensive companies, like Koch or ExxonMobil, would also be impacted significantly.

EDIT: The counterpoint is that a gas tax in particular is quite regressive. The poor pay a larger portion of their income toward necessities like fuel to drive to work. They also are less likely to be able to afford that Tesla. Entry-level service workers can't work from home. They might be commuting large distances from cheaper outlying areas. There are many reasons why (if not managed properly) a carbon tax could hurt the wrong people.

It still seems like the right idea to me, though! We need to avoid calling it a 'tax' though, to avoid the Grover Norquist influence...