Walmart has over 4,600 stores in the US. Between its Supercenters (187,000 sq ft on average), Discount Stores (104,000 sq ft), Neighborhood Markets (42,000 sq ft), and Sam’s Clubs (134,000 sq ft), that’s a lot of shopping aisles to keep clean.

That might be why the US’s largest private-sector employer is testing out self-driving mechanical floor scrubbers during overnight shifts in five of its stores near its headquarters in Bentonville, Arkansas, according to a post by LinkedIn managing editor Chip Cutter. The machine, named EMMA, roams around the store like the cross between a Zamboni and a Roomba.

The machine is manufactured by a company called International Cleaning Equipment, and is normally driven by a human, but after modifications from the robotics startup Brain Corporation, the seat sits empty. Much like a self-driving car, EMMA uses cameras, sensors, and LiDAR, as well as AI, to navigate and avoid obstacles—but instead of navigating roads and avoiding people and other cars, EMMA works its way through retail store aisles and dodges other staff.

A Walmart spokesperson told Quartz these tests are part of a very early “proof of concept” stage, and won’t be adopted widely in the immediate future. But the move has already caused anxiety among some employees, Cutter reports. Though the retail giant has taken progressive steps in recent years to boost employee pay and revamp its vacation and sick leave, it has in parallel eliminated swaths of jobs through increasing automation. Last year, for example, it nixed roughly 7,000 store accounting and invoicing positions, which the Wall Street Journal noted (paywall) were mostly highly coveted, well-paying jobs held by long-tenured employees.

The spokesperson said Walmart is unaware of any employees expressing discontent. According to Walmart, the maintenance associates working directly with the self-driving floor scrubbers are excited about getting an opportunity to work with robotics. They have learned to program EMMA and are involved in monitoring, cleaning, and maintaining it on a day-to-day basis, the spokesperson said, emphasizing that the bot is not capable of fully operating without human assistance.

Other recent actions taken by Walmart suggest the company is relatively sensitive towards concerns about reduced job opportunities for humans. In October, the company introduced shelf-scanning robots in 50 US stores to help, rather than replace, employees tasked with replenishing missing and misplaced inventory. The company also says that as it adds more machines, it will find new roles for employees whose jobs get automated.

Even so, it’s easy to imagine a future where the retail giant won’t need all of the 1.4 million people it currently employs in the US. And should that happen, it would be a major hit on US employment: 1.4 million is 1% of the entire workforce.