NEW YORK — A U.S. company is asking its workers to act as guinea pigs for an under-the-skin chip that lets them buy snacks, use office equipment and open doors.

The company, Three Square Market, says the chips are not mandatory. It expects over 50 staffers to get a chip between their thumbs and forefingers at an Aug. 1 “chip party” at the company’s River Falls, Wisconsin, offices.

Implants that act like swipe cards are already used by some European companies . They’ve raised privacy concerns because they can track employee purchases and whereabouts and are harder to ditch than an ID card.

Three Square Market expects the chips to become popular in its business. It provides self-service convenience stores for companies so employees can buy snacks and is a vendor to jails.