(Updates to close)
May 23 (Reuters) - Shares in Australia's 'big four' banks weakened on Tuesday as a result of a government tax proposal, dragging the benchmark index to a lower close.
The S&P/ASX 200 index ended 11.005 points or 0.19 percent lower at 5,760.2 points.
The country's largest lender, Commonwealth Bank of Australia fell 0.41 percent, while Westpac slipped 1.03 percent.
The banks issued a strongly worded statements, saying the new tax would result in A$1 billion of additional costs annually, and would also hurt customers and shareholders.
Iron miner BHP Billiton was also among the worst performers on the index, slipping to its lowest in nearly three weeks after ore prices slipped 1.72 percent on the Dalian Commodity Exchange.
Fortescue ended 2.05 percent lower, while Rio Tinto closed 0.63 percent down.
New Zealand's benchmark S&P/NZX 50 index shed 0.34 percent or 24.8 points to finish the session at 7,384.7.
The country's largest provider of mobile phone services, Spark New Zealand, led losses, declining 1.87 percent to post its biggest drop in six weeks. (Reporting by Aparajita Saxena in Bengaluru; Editing by Simon Cameron-Moore)