Apple has been ordered to pay back 13 billion euros (£11 billion) over its Irish tax deal.
We take a look at the tax arrangements that led to the EU Commission's ruling and which companies could be next in the firing line.
What sort of arrangement did Apple have with Irish authorities?
The EU Commission's investigation was launched in 2014 under the suspicion that Irish authorities were purposefully miscalculating and ultimately underestimating Apple's taxable profit on products like iPhones and iPads.
The multinational corporation is said to have secured a tax advantage not available to other companies, which ultimately amounted to state aid and breached EU antitrust law.
Apple was found to only be paying 1% tax on its European profits in 2003 and 0.005% in 2014.
Both Irish authorities and Apple have repeatedly denied breaching state aid rules.
Why does the EU's ruling on Apple matter?
The sheer size of the case is drawing attention. In October, the EU Commission ordered Starbucks and Fiat to pay 20 to 30 million euros for benefiting from so-called sweetheart tax deals in the Netherlands and Luxembourg.
That is compared with the latest ruling, which is calling on Ireland to recoup 13 billion euros (£11 billion) in unpaid taxes from Apple.
The case has also irked the US Treasury, which earlier this month published a paper accusing EU authorities of unfairly targeting US companies in antitrust probes.
Lewis Crofts, global chief correspondent at antitrust trade publication Mlex, explained that the US is worried that Apple's cash won't make it back to the US. "They say 'it's our money, you have no right to take it'. That's the big fight."
Will Apple pay?
Apple will appeal the ruling, saying it is confident the order will be overturned.
The tech giant accused the EU Commission of threatening future investment and job creation in Europe, where it currently employs 22,000 people.
While the ruling would ultimately benefit Irish government coffers, Mr Crofts says Ireland will also appeal against the EU Commission's decision.
"The irony is that there will be domestic pressure to accept this money, but what Ireland knows is that, in this instance, the decision makes it much less attractive to invest in," Mr Crofts said.
Which companies will be targeted next?
A case this size is unlikely to come up again, but there are other US companies in the firing line.
EU authorities are currently investigating Amazon and McDonald's for similar tax deals it deems illegal. Those rulings could be doled out in the next six to 12 months.
But potentially any company that is deemed to have received a special deal from a European government could be end up targeted by antitrust watchdogs in the near future, Mr Crofts said.