The city began enforcing its ban on Styrofoam Monday following a six-month warning period — but some food cart vendors claimed they didn’t know anything about it.

“I’m here every day and no notification,” Mohammed Ali, a vendor with two carts at Bryant Park in Manhattan, told The Post on Monday.

Ali, 25, was still slinging hot dogs and gyros in the banned material on 42nd Street and Sixth Avenue, unaware he could be slugged with a hefty fine under the new law.

The city banned single-use Styrofoam cups, plates and trays on Jan. 1, but gave businesses a six-month grace period which ended on July 1.

The department said it sent more than 130,000 mailers to businesses warning them of fines which start at $250 for the first offense, $500 for the second and $1,000 for subsequent violations.

But it seems many of the Big Apple’s beloved food cart vendors didn’t get the memo.

“I have no idea about it,” an employee at Kimo’s Halal Food on 45th and Sixth Avenue said.

Some vendors in Midtown said they were warned last week by the nonprofit Street Vendor Project, while others learned through word of mouth.

Mohammed Nabi, 45, a vendor at Water Street and Maiden Lane in Lower Manhattan, said the change would hurt his already thin bottom line.

“The Styrofoam containers were $12 and now it’s going up to $18. It doesn’t sound like a lot, but it adds up,” Nabi said.

A DSNY spokesperson said staff began issuing fines on Monday but would not say how many tickets were handed out for foam violations.

New York City stores and food-service businesses are now prohibited from offering, selling and possessing single-use foam food containers such as takeout clamshells, plates and cups.

The material is not recyclable and is instead collected as trash.

“Single-use foam has littered our streets, sidewalks and parks or ended up in our landfills for too long,” City Council Speaker Corey Johnson said in a statement Monday.

Dive bars famed for serving beer in 32-ounce Styrofoam cups were prepared ahead of time but bemoaned the changes.

“It’s the end of an era,” Samantha Horan, the owner of Farrell’s Bar & Grill in Brooklyn, said last week.