Auditors doing whatever they can to stare down regulators
They are some of the Ireland's biggest employers and their market share exceeds 85pc in the majority of EU nations, so it's no wonder that the Big Four attract fierce attention from regulators.
The group consists of PwC, KPMG, Ernst & Young and Deloitte, who made close to €1bn in Ireland last year.
Managing partners at the firms have more to celebrate than healthy revenues; they avoided a very close call earlier this year, after new proposals by the UK Competition Commission fell short of requiring FTSE 350 listed companies to switch auditors every year.
First suggested in 2011 by EU financial services chief Michel Barnier, it was originally thought the proposals would require banks, insurers and listed companies to rotate the audit firm they used every six years, with a four-year gap before the firm could be rehired. The rotation period could be extended to nine years if a company uses more than one auditor.
Regulators embarked on wide-ranging reviews of audit rules following the collapse of Lehman Brothers, which the European Commission said raised doubts about the quality of company audits.
Their investigation was also spurred on by the anti-competition issues surrounding the high market share enjoyed by just a smattering of firms.
Documents published in June 2010 show that some UK companies' banking covenants require them to use one of the Big Four.
But the rules ultimately issued by the UK Competition Commission earlier this year only required companies to put their audit contracts out to tender every five years, and previous auditors can still apply for the new role.
The Big Four, unsurprisingly, were still less than pleased: Deloitte said five-year tendering was unlikely to improve audit quality or increase competition, while Ernst & Young said competition between audit firms was already healthy and robust. KPMG said regular tenders would cost far more than the £30m the competition body has estimated in total for companies and accountants annually.
And the decision still faces being overruled by a draft European Union law now undergoing approval.
Regardless of what exactly is decided, any new law will affect Irish companies like CRH, Kenmare and United Drug, which are listed in London.
Auditors' responsibilities as well as their market share have also come under the microscope of late.
The joint administrators of Quinn Insurance are currently suing PwC for around €1bn, alleging the firm negligently audited its account over several years. It is the largest ever action taken against an Irish auditor.