Tuesday's ruling that the government aid must be re-examined by an EU appellate court is also a victory for France Télécom rival Bouygues SA, which sought to annul a lower court ruling that France's promise of support when France Télécom was teetering on bankruptcy did not qualify as state aid.

"While it is true that France Télécom did not sign the loan agreement sent to it, the company could nevertheless have signed it at any time, thereby acquiring the right to obtain immediate payment of the sum of €9 billion," the Luxembourg-based Court of Justice of the European Union said in a statement.

The case dates back to 2002, when the French state sent a draft shareholder loan contract to incumbent France Télécom, which neither signed nor implemented it.

In July of that year, the French minister of economic affairs also said publicly that the state shareholder "will behave like a prudent investor and take appropriate steps if France Télécom were to face any financing problems." A few months later, French authorities declared that the state would contribute to the strengthening of France Télécom's capital base and would take steps to keep it from facing financial difficulties.

In August 2004, the Commission found that the promised shareholder loan constituted illegal state aid incompatible with EU law, since it helped the state-owned company increase its financing and reassured the market about the company's ability to meet its debt obligations. The Commission also noted that the minister's July 2002 public statement prevented France Télécom's rating from being downgraded to junk status.

But since the Commission could not evaluate the impact of the largely notional aid, it could not order it to be recovered, as is the norm in state aid cases.

The Commission's decision was annulled by an EU appellate court in May 2010. It found that although the government declarations had given France Télécom an advantage, they did not lead to a corresponding reduction in the state budget. It also found that the regulator should have examined the impact of each government statement individually, and required a close connection between an advantage for a company and the commitment of state resources.

On Tuesday, the Court of Justice found that the lower court erred in law, and ordered a new review by the lower court.

Cédric Kaczmarek, a Brussels-based lawyer at Hogan Lovells International LLP, said Tuesday's ruling could have a freezing effect on EU governments keen to speak publicly about supporting their companies during the financial crisis.

"Public figures will have to think twice before declaring they will support an undertaking, especially a state-owned one, because of the crisis," he said.