Gov. Andrew Cuomo is doing a fine job of siding with straphangers — rhetorically. But the guy who controls the MTA needs to do more than voice the public’s anger and frustration.

He has repeatedly called on the MTA to handle the growing homeless problem, and just came out in full support of the NYPD’s push to get serial subway pervs banned from the system for life.

But, again, the gov has personally chosen (or signed off on) the agency’s entire top management team. Heck, the new chief MTA spokeswoman, Abbey Collins, is a Team Cuomo alum.

Yes, the MTA board can slow or stop major change. But if its members try to stand against “taking action against these repeat [perv] offenders” as the gov demands, he has the bully pulpit to make them pay.

Similarly, Cuomo has a point in implicitly slapping the mayor for the MTA’s homeless problem, calling it a “quality-of-life [issue] that has now walked down the stairs from the street into the subway.”

But, as the gov himself also says, “The MTA is responsible for the MTA. . . . They have a police force. They have 70-something-thousand employees. They are responsible for their rules and regulations.”

To be fair, Cuomo’s Subway Action Plan managed to stabilize a system that was failing critically just two years ago. But when it comes to really changing how the subway and the MTA’s other divisions operate, the biggest single issue is the MTA’s unions.

And it’s not just labor contracts, with work rules that often tie managers’ hands in ridiculous ways. It’s an entire culture.

All the MTA’s middle managers all know the unions will still be there when Cuomo leaves office, even if he serves five terms. Unless they know they’ll have firm support all the way up the chain of command, few will stick their necks out just to make the trains run on time.

That may be why the gov is also speaking up for the workers, citing, “One hundred assaults, stabbings, punchings, violence against MTA employees. These are public servants. There are people who are doing a very difficult job.”

But in the end, the workers and the riders need to know that Cuomo’s going to offer more than just talk.