Moody's Investors Service yesterday revised the rating outlooks of five banks in Australia, including all major banks, to negative from stable.The banks with revised outlooks include Australia's four major banks, ANZ, Commonwealth Bank, National Australia Bank and Westpac. All four banks are rated Aa2 for senior unsecured debt.Moody's has also revised the rating outlook of Members Equity Bank Limited (ME Bank). ME is rated A3 for senior unsecured debt.Thirteen more banks, many of them mutuals, sidestepped a negative outlook. This group also includes Bendigo and Adelaide Bank and Suncorp Bank.The credit ratings agency said "the outlook change for Australia's four major banks reflects Moody's expectation of a more challenging operating environment for banks in Australia for the remainder of 2016 and beyond, which could lead to a deterioration in their profit growth and asset quality, as well as an increase in their sensitivity to external shocks."Among the trio of principal rationales outlined by Moody's was the perennial cynic's favourite, housing prices. Moody's, in neutral language, summed this up as "continued concerns regarding the banks' exposure to tail-risks in the Australian housing market, which has been characterised over the recent past by strong price appreciation and rising household debt."The wider macroeconomic background was mentioned first by Moody's in its list, and it's a topic bound to resonate in the debate over the pros and cons of a Royal Commission into banking in Australia."The rating action reflects Australia's ongoing economic transition which, despite stable aggregate economic growth, has resulted in low nominal income and wage outcomes and persistently low interest rates, exerting in turn downward pressure on the banks' profit growth," Moody's said.Third, Moody's cited "rising bad debt within parts of the banks' lending portfolios, in part reflecting these [other] pressures."Moody's added commentary on the outlook change for ME Bank. It said this reflected "ME's high reliance on wholesale funding and potential pressures on capitalisation, given the bank's growth ambitions, which are aggressive relative to its ability to generate organic capital. These factors could place the bank in a weaker position to withstand the operating environment challenges noted above."For 13 other Australian financial institutions, Moody's said it considered their balance sheet settings "to be sufficient to withstand deteriorating operating conditions at their current rating levels. These institutions include Australia's regional banks, the subsidiaries of foreign banks operating in Australia, mutual banks, credit unions and building societies, and other selected banks."