The Advocate General of Europe's highest court has said a €1.06 billion fine against the US giant Intel should be subject to a judicial review.
The announcement could see the fine being reduced or overturned by a lower court.
The European Commission had fined Intel the record amount in 2009 after finding the company guilty of abusing its dominant position in the computer chip market between 2002 and 2007.
The Commission had accused Intel of paying rebates to personal computer makers like Dell, HP and Lenovo so they would favour Intel microchips over those of its rivals.
Intel appealed the decision but in June 2014 the General Court of the European Court of Justice upheld the fine, saying it was proportionate to the alleged antitrust behaviour of the company.
The US multinational, which employs over 4,500 people in Ireland, then appealed the General Court finding to the European Court of Justice.
This morning the Advocate General of the higher court agreed with five of the six grounds of appeal that Intel had submitted.
He issued an opinion saying that the General Court had "erred in law" when it upheld the European Commission's fine.
In particular, the General Court had ruled that the rebate deals offered to computer makers Dell and Lenovo were "exclusive" in nature.
As such, according to the Advocate General, the lower court had not fully explored whether such rebates did, in fact, restrict competition in the microprocessor market.
In this morning's opinion he said that in practice the European Court of Justice had consistently taken into account "all the circumstances" when concluding if certain conduct amounted to market abuse.
He said that, according to the General Court's interpretation of "exclusivity rebates", even where a company was not capable of restricting competition, it would, be caught in a "blanket prohibition".
This, he said, would have happened even if in some cases the conduct of a company actually favoured competition.
The Advocate General found that the General Court was mistaken in declaring that "exclusivity rebates" should be regarded as a separate and unique category of rebates without taking into account "all the circumstances" in order to establish whether Intel had abused its dominant position or not.
Overall, he said, the General Court had not been able to establish that the rebates and payments made by Intel to Lenovo and Dell had had an anti-competitive effect.
The Advocate General also said that for the rebates paid to Dell and Lenovo to be "exclusive", both companies would have been obliged to buy "all or most" of its requirements from Intel.
However, it was not clear that this was the case.
In fact, he concluded, HP and Lenovo could still have purchased significant quantities of microprocessors from Intel's chief rival Advanced Micro Devices.
The Advocate General also said that the General Court had not properly taken account of complaints by Intel that an interview carried out by the European Commission with a Dell executive when investigating the case was not recorded.
He said that such a "procedural irregularity" could not have later been remedied by the Commission by a written note, since such a note would not have recorded the "substance" of the interview.
The appeal by Intel now awaits final judgment by the European Court of Justice, expected within three to six months.
In 80% of cases, the final judgment is in line with the opinion of the Advocate General.
If the ECJ concurs, the case would be sent back to the General Court for review, and the record €1.06bn fine against Intel could be reduced, or overturned completely.
The case comes amid ongoing criticism by American multinationals of antitrust decisions taken by the European Commission's powerful competition arm.
In August the Commission declared that Apple owed the Irish government €13bn plus interest for its allegedly favourable tax arrangements with Ireland.
The Irish Government has said it will appeal that decision.