The supermarkets' challenge against the European Commission underlined the recent willingness of companies to fight what they say are excessive demands and regulatory overreach by the EU competition enforcer.
The Commission in February 2017 ordered the companies and their subsidiaries to submit to an inspection.
The EU competition enforcer last year subsequently opened an investigation into the supermarkets' purchasing alliance set up in France in 2014, saying that this could have been used to illegally coordinate their actions.
The supermarkets then took their case to the Luxembourg-based court, disputing the legality of the seizure and copying of data relating to the private lives of their employees and managers and the refusal to return those data.
The General Court agreed with some of their arguments and annulled part of the Commission's inspection decisions. However, it also upheld the EU system for conducting antitrust raids.
"The Commission has failed to show that it had sufficiently strong evidence to suspect exchanges of information concerning the future commercial strategies of the undertakings," judges said.
The tie-up was dissolved in 2018 when Casino and France's Auchan [AUCH.UL] agreed to a global buying deal.
Buying tie-ups have become more popular in recent years as a tactic to counter online retail giant Amazon and rivals offering price discounts.
The cases are T-249/17 Casino, Guichard-Perrachon and AMC v Commission; T-254/17 Intermarché Casino Achats v Commission; and T-255/17 Les Mousquetaires and ITM Entreprises v Commission.
(Reporting by Foo Yun Chee; Editing by Kirsten Donovan)
By Foo Yun Chee