Apple will be accused of prospering from illegal tax deals with the Irish government for more than two decades when Brussels this week unveils details of a probe that could leave the iPhone maker with a record fine of as much as several billions of euros.

Preliminary findings from the European Commission’s investigation into Apple’s tax affairs in Ireland, where it has had a rate of less than 2 per cent, claim the Silicon Valley company benefited from illicit state aid after striking backroom deals with Ireland’s authorities, according to people involved in the case. Apple, which has operated in Ireland since 1980, maintains that its agreements with Ireland did not break any laws. “There’s never been any special deal, there’s never been anything that would be construed as state aid,” Luca Maestri, Apple’s chief financial officer, told the Financial Times.

The attack on the tax practices of the world’s richest company follows last year’s US Senate hearings, where it emerged that Apple shifted billions of dollars in profits out of the US to international subsidiaries with no declared tax residency. Based on its concerns, the commission has decided to open an in-depth investigation of arrangements between Apple and the Irish authorities dating back to 1991. It is part of a wider crackdown on what Joaquín Almunia, the EU’s competition commissioner, has called “aggressive” tax avoidance.