But this week's appeal concerns the 2.4bn euro fine handed out in 2017 against Google for allegedly favouring its own price-comparison shopping service against those of smaller European rivals.
Google will seek to nullify the first of three strong European Union antitrust fines in the second highest court in Europe in a historic case that could determine how EU enforcers face the U.S. tech giants. UU.
Commission lawyer Nicholas Khan swatted away Google's arguments, saying this was a clear case of a company using its dominance to give itself an advantage in other markets.
However, Google rejected regulator's findings and challenged the decision in the EU's General Court in Luxembourg.
In a statement to the BBC, Google is arguing that the fine has no legal or economic merit and that their shopping ads have always been helping people find needed products quickly and easily, as well as assisting sellers reach a wider audience.
The first significant fine against Google was levied in 2017, when the European Commission fined it 2.4bn euros (£2.01bn) after it ruled that Google had thwarted rivals of shopping comparison websites.
Two further decisions for different issues since then have lifted the total penalty to 8.25 billion euros, four times more than Microsoft's (MSFT) EU fines of 2.2 billion euros.
The EU commission will give testimony alongside complainants who accuse Google of having smothered their business.
The success of Google's appeal might depend on whether it can prove that self-preferencing is not anti-competitive, and whether Amazon and eBay are to be seen as Google's competitors.
"Our traffic decreased considerably, which created a vicious circle with merchants who no longer saw us as an alternative to Google Shopping", said Laurent Godfroid, a lawyer for Twenga, a rival to Google Shopping.
Lawyer Thomas Vinje for British price-comparison shopping service Foundem, whose complaint triggered the European Union investigation, said Google's product would never have gained prominence if Google had treated it the same way as rival products.
The document also said competition enforcers were considering regulating the behaviour of dominant companies as a preventive measure, a move that would address concerns that regulatory actions sometimes come too late to fix the harm suffered by smaller rivals.
The EU has already said it was looking into Google's similar push into job ads.