Commonwealth Bank is facing another legal battle after ASIC yesterday launched a civil action in the Federal Court, alleging that traders employed by the group rigged rates in the bank bill market.While CBA is the fourth Australian bank to be hit with civil proceedings for alleged rate manipulation, the regulator's concise statement of claim in this case includes a bombshell allegation that NAB, ANZ and Westpac were not called to defend.According to ASIC, CBA's senior management was aware of unconscionable practices used by the bank's traders to manipulate the bank bill swap rate(BBSW) over a ten month period starting in January 2012."The fact that CBA traded with purpose of affecting BBSW in a manner favourable to it (including preventing or restricting BBSW moving in a manner contrary to its interests) was known by senior management of CBA," the regulator alleges in its concise statement of claim.The CBA executives allegedly aware of the unconscionable conduct were not named in the court documents published on ASIC's website on Tuesday.However, the allegation could be particularly damaging for the bank, which has embarked on a program to restore its internal culture and public standing following a wave of scandals in the last three years.That remedial program was a recurring theme of a press conference held on Monday to announce Matt Comyn as the next chief executive of the group.In a statement issued on Tuesday night, CBA indicated that it would defend the new legal claim."ASIC has today filed a claim against the Commonwealth Bank of Australia that alleges the bank engaged in market manipulation and unconscionable conduct in relation to the Bank Bill Swap Rate," the bank said."Commonwealth Bank has fully co-operated with ASIC's investigation over the last two years."Commonwealth Bank disputes the allegations made by ASIC."As this matter is before the courts, it is not appropriate to comment further at this time."Board chair Catherine Livingstone said on Monday that the focus of the remedial program was to put the wellbeing of customers at the centre of what the bank does and unequivocally fulfil its regulatory obligations.The ASIC legal action could disrupt that agenda if the court finds senior executives still employed at the bank did nothing to prevent traders from engaging in rigging of the swap rate.ASIC claims that CBA profited from the alleged activity without telling customers or counterparties of the risks that its unconscionable practices posed to their financial interests."... CBA, in trade or commerce, engaged in unconscionable conduct by entering and offering to enter into BBSW Referenced Products with customers or counterparties, other than Prime Banks, knowing or believing that CBA would likely engage in a practice detrimental to the financial interests of its counterparties," ASIC alleges in its concise statement of claim.While most of the legal breaches alleged by the regulator have been brought under the unconscionable conduct provisions of the Corporations Act, ASIC also claims that the bank engaged in misleading and deceptive conduct and failed to train its traders adequately.ANZ and NAB last year each coughed up