On Monday, Mayor Bill de Blasio and Senator Charles Schumer handed out flyers in the subway to tell straphangers about a tax break that could save each of them hundreds of dollars a year — but many don't even know about it.

There's a new way for straphangers to swipe and save.

"All you have to do is get your employer to fill out a form and you get it off your taxes," Schumer said.

Not that many New Yorkers are even aware of the tax break.

"Didn't even know it existed," said one straphanger. "Yeah, I think anything that benefits the commuters or even New Yorkers, a lot of these are kept secret."

"Sometimes we are ignorant for these situations," said another. "I never hear that."

Mayor de Blasio and Senator Schumer took to the subway Monday to tout the expanded benefit.

"You can save up to $800 a year!" the mayor told riders.

Under legislation pushed through by Schumer last month, employees can now spend as much as $255 in pre-tax income each month on transit expenses, up from $130 a month.

And under a new city law, companies with at least 20 full-time workers must allow their employees to set aside pre-tax income for transit costs.

The pre-tax benefits aren't limited to riders of only the city's buses and subways. They're also available to those who rely on the commuter railroads, Amtrak, eligible water taxis and ferry services. For more information, call 311.

Schumer said the benefit makes sense for the millions of New Yorkers who use mass transit daily.

"It was a great injustice, because you could always do this if you drove to work," Schumer said.

Advocates from the Riders Alliance say not enough commuters have been taking advantage of the tax break, though there are no figures on precisely how many skip the benefit.

"I think people didn't know how easy it was to sign up it's really easy," said Rebecca Bailin, with the Alliance. "And I think that there are many employers that did not provide it as a benefit."

Now they have to.

"450,000 more New Yorkers will be eligible for commuter benefits," Bailin said.

Employers and employees can learn more about the law by visiting the city's web site.