Online marketplace eBay has filed a US lawsuit against Amazon, claiming the retail giant used its internal messaging system to poach sellers.
The lawsuit alleges that Amazon representatives signed up for eBay accounts and sent messages to persuade users to sell their goods on Amazon, which eBay said violated its user agreement.
Ebay described it as an "orchestrated, coordinated, worldwide campaign" to "illegally lure eBay sellers to sell on Amazon".
The legal complaint says that Amazon representatives asked eBay sellers to talk on the phone to avoid detection.
Ebay says it wants to stop Amazon misusing its messaging platform and to pay it an unspecified sum.
Amazon declined to comment.
Ebay first made public its complaint earlier this month that it had uncovered "a unlawful and troubling scheme on the part of Amazon to solicit eBay sellers to move to Amazon's platform" and demanded that it ended the activity.
Seattle-based Amazon said at the time that it was conducting a thorough investigation.
Both companies rely on independent sellers to boost their revenue.
Last year, for the first time more than half the items sold on Amazon were from third party sellers.