The accountancy watchdog has slapped PwC with a £5m fine for misconduct in relation to its 2009 audit of Connaught.
The Financial Reporting Council (FRC) said that PwC and Stephen Harrison, a retired audit partner at the firm who was fined £150,000, had been "severely reprimanded" following an investigation.
The reprimands relate to PwC's audit of Connaught, a FTSE 250 company that went into administration in 2010.
The charge relates to areas of mobilisation costs, long-term contracts and intangible assets.
PwC was ordered to pay the FRC's legal costs and to make an interim payment on account of £1.5m.