EBay Inc. (EBAY.O) accused rival Amazon.com Inc. (AMZN.O) of poaching sellers on its site around the world by infiltrating the company’s internal message system.

About 10 days ago, an EBay seller alerted the company to the alleged campaign after the person was contacted by an Amazon employee, under false pretenses, attempting to recruit the person to switch platforms, according to a person familiar with the investigation. This sparked an internal EBay probe that uncovered recruiting activity spanning several years and continents, with Amazon employees creating accounts with EBay and using the member-to-member email system, the person said, asking not to be named discussing details that aren’t public.

On Monday, EBay sent a cease-and-desist letter to Amazon accusing the retail giant of violating California’s Comprehensive Computer Data Access and Fraud Act, as well as EBay’s user agreement and policies.

"We have uncovered an unlawful and troubling scheme on the part of Amazon to solicit EBay sellers to move to Amazon’s platform," an EBay spokesman said in a statement. "We have demanded that Amazon end its unlawful activity and we will take the appropriate steps, as needed, to protect EBay."

The Wall Street Journal reported earlier on the probe. Amazon said it is “conducting a thorough investigation of these allegations.”

The news of the poaching comes less than a month after it was reported that Amazon employees are offering sellers confidential internal data and other services in exchange for a fee.

EBay and Amazon are fierce competitors that rely on independent merchants that sell on their sites. Amazon has more customers, sales and faster growth than EBay, but some sellers still prefer the EBay platform since it is a pure marketplace, meaning EBay doesn’t compete with its merchants for sales like Amazon. EBay also lets merchants communicate directly with customers and post email addresses and phone numbers on the site, while Amazon controls the overall shopping experience on its site and discourages merchants from communicating directly with Amazon shoppers.