Maurice Blackburn Lawyers has launched "the first class action against a Big Four bank since the publication of the Hayne royal commission report," with Westpac targeted over its responses to alleged breaches of responsible lending laws.The plaintiff law firm said the class action was being run in the Federal Court on behalf of people who, after 1 January 2011, were given "unsuitable loans" by Westpac, in breach of its responsible lending obligations.A note on the law firm's website advises customers who banked with one of Westpac's companies: St George, RAMS, Bank of Melbourne and BankSA is ineligible to win.The law firm said the action "has been undergoing careful preparation for months" and is being supported by Harbour Fund IV. Principal lawyer and managing partner with Maurice Blackburn, Ben Slade, said: "This case will seek to prove that Westpac failed to comply with its obligations and that this failure caused substantial losses for many consumers."Lead litigants (ie, one of the test cases) will be Michelle and Ian Tate. They will argue Westpac failed to carry out any reasonable enquiries, relying on information provided by a mortgage broker, which saw the bank lend more than A$1.8 million to the Tates - described as a "family of five with one regular income". This over-extended them resulting in the loss of all their properties "save for a block of land," they said. A crucial part of the responsible lending regulations that came into operation from 2011, were that: "A consumer who has suffered loss or damage, or is likely to suffer loss and damage, as a result of a contravention of responsible lending obligations, may seek damages and other compensation orders."The announcement of the class action appeared to have blindsided Westpac, judging from its response: a brief statement to the ASX late yesterday. Westpac confirmed "it is aware of the class action against it in regard to responsible lending laws being brought ... and will be defending the claims against it".Westpac said it "takes its responsible lending obligations very seriously" and "works closely with customers who experience financial difficulty to provide tailored assistance as required".