Walmart Inc. (WMT  ) has filed a lawsuit against BJ's Wholesale Club (BJ  ) alleging the theft of patented technology related to the "Scan & Go" service.

Walmart's "Scan & Go," mostly used at Sam's Club stores, allows customers to scan items using their smartphone camera as they shop. Users of Scan & Go can then pay from their phone and skip waiting in line. BJ's Wholesale club, according to Walmart's filings, "copied" Walmart's app entirely.

It's worth noting that Walmart isn't the only retailer to have brought this technology to market, however. Among others, many regional grocers such as Wegman's, Giant Eagle, and H-E-B have developed their own apps that feature phone scanning. Some competing versions require an extra step of scanning at a self checkout kiosk.

"Express Pay is strikingly similar to Sam's Club's Scan & Go, offering nearly identical functionality," Walmart wrote of its competitor's "Express Pay is an apparent copy of Sam's Club's Scan & Go, merely changing the in-app colors and changing the name from Scan & Go to Express Pay."

Walmart claims that BJ's theft of the technology has caused it "significant damages and irreparable harm," The retailer is seeking undisclosed damages and is seeking to halt BJ's use of its patented technologies. Neither company has spoken to members of the media on the matter.

Walmart's Scan & Go deployment came before the COVID-19 pandemic but saw widespread use as anxious consumers looked for ways to shop while socially distant. Scan & Go, curbside pickup, and Walmart's strong ecommerce presence were just some of the retailer's strengths during the pandemic that helped it remain profitable during a time of economic volatility. The company's latest Q4 earnings report was strong as well, with promising guidance.

Walmart shares made slight gains on Friday, edging in 0.62% before close, but were down 1.36% for the week. BJ's shares were down 0.50% on Friday, and 2.1% for the week.