Ernst & Young has been banned from taking on new clients in the US after regulators questioned its relationship with software company PeopleSoft.
Judge Brenda Murray said that E&Y should not accept new auditing work for six months from Securities and Exchange Commission-listed companies.
E&Y is not expected to appeal the ruling, which includes a $1.7m fine.
The SEC was concerned about E&Y’s role as auditor of PeopleSoft because the two also had a business agreement.
Explaining her decision, Judge Murray said that “E&Y engaged in improper professional conduct because it violated applicable professional standards for auditors by conduct that was both reckless and negligent”.
“E&Y’s misconduct was blatant,” she continued.
“There is nothing in this record that shows that E&Y is willing to accept the auditor independence rules applicable to business relationships with audit clients”.
The ruling is another blow to the reputation of the accountancy firm, which is a member of the so-called Big Four that have dominated the industry in recent years.
Their working practices have been more closely scrutinised following the scandals that surrounded companies such as energy-trading giant Enron.