The city wants to add new letters to its restaurant-grading system: GPS.

Department of Health officials are cooking up a plan to outfit every mobile food vendor in the city with a “location-sharing device” so city workers have an easier time tracking down carts for inspections.

Currently one-fifth of the city’s 5,500 licensed food trucks go unchecked because inspectors cannot find them, according to the proposal.

But critics say the plan is a recipe for disaster, because federal officials could use it against primarily immigrant vendors.

“We’re really concerned about this info falling into wrong hands given the political climate and the harsh stance that federal authorities have been taking,” said Matt Shapiro of advocacy group the Street Vendor Project. “The vast majority of vendors are immigrants.”

Vendors called it an overreach.

“It feels more like Big Brother,” fumed Adam Disilvestro, 38, owner of Diso’s Food Truck on Sixth Avenue and 48th Street in Midtown. “So now I have to have a GPS tracker because they can’t do their job?”

A Health Department spokeswoman said the city would foot the bill for the devices. She said DOH would only use the GPS info to conduct inspections, and is “prohibited from sharing the location information with anyone unless legally required to do so.”