BRUSSELS • In the latest setback to European Union efforts to tackle corporate tax avoidance, a court on Wednesday annulled a ruling by the European Commission that a tax deal between Amazon and Luxembourg’s government amounted to illegal state support.

The EU’S executive branch ordered the U.S. online retailer in 2017 to pay around $300 million in back taxes to Luxembourg. But judges at the EU’S General Court said the European Commission didn’t prove “to the requisite legal standard that there was an undue reduction of the tax burden of a European subsidiary of the Amazon group.”

Amazon said it welcomed the decision, which is “in line with our long-standing position that we followed all applicable laws and that Amazon received no special treatment,” the company said. “We’re pleased that the Court has made this clear, and we can continue to focus on delivering for our customers across Europe.”

The European Commission’s decision related to Luxembourg’s tax treatment of two companies in the Amazon group: Amazon EU and Amazon Europe Holding Technologies. Margrethe Vestager, the EU official in charge of antitrust issues, argued Amazon had unfairly profited from special low tax conditions since 2003 in tiny Luxembourg, where its European headquarters are based. As a result, almost three quarters of Amazon’s profits in the EU were not taxed, she said.

“We will carefully study the judgment and reflect on possible next steps,” Vestager said.

Luxembourg and Amazon challenged the decision with the EU’S General Court.

The EU has taken aim at deals concluded between individual countries and companies used to lure foreign multinationals in search of a place to establish their EU headquarters. The practice led to EU states competing with each other and multinationals playing them off one another.

Judges at the General Court have backed the European Commission in several cases, but the EU’S efforts to crack down on tax deals suffered setbacks in cases involving Starbucks and Apple. Wednesday’s ruling can be appealed.

The EU remains at odds with Amazon on other issues relating to competition. Last year, EU regulators filed antitrust charges against the e-commerce company, accusing Amazon of using its access to data from companies that sell products on its platform to gain an unfair advantage over them.

In another judgment, the General Court found the existence of a tax advantage in rulings granted by Luxembourg to companies in the Engie group, a French multinational electric company. Three years ago, the European Commission found Luxembourg allowed two Engie group companies to avoid taxes on almost all their profits for about a decade and the country should recover about 120 million euros in unpaid tax.