* Macquarie doesn't rule out headquarters move
* Bank tax to lower Macquarie's global earnings by 4 pct
* Tax alone not enough to justify shifting HQ -analyst (Adds statement from Macquarie on tax impact)
By Jamie Freed
SYDNEY, June 2 (Reuters) - Macquarie Group Ltd MQG.AX , battling a surprise $4.6 billion tax on Australia's lenders, left open the option of moving its headquarters abroad on Friday, baffling analysts and lawyers who warned a costly shift may do little to avoid the levy.
Australia shocked banks and investors last month with a new balance sheet tax that hits all lenders with more than A$100 billion ($74 billion) of total liabilities.
The country's top investment bank also joined Australia's Big Four lenders in voicing its displeasure with the tax, estimating it would cut its global earnings by about 4 percent and warning of possible unintended consequences for local earnings.
Macquarie has two-thirds of its business and most of its staff outside Australia, but the issue of where its headquarters should be located has not been actively or publicly debated.
An unsourced report in the Australian Financial Review said on Friday, however, that Macquarie had told at least one of the major political parties it was now canvassing options for relocating outside Australia as a result of the tax.
A spokeswoman for the bank said in response to the report:
"As we have said over the years, Macquarie consistently looks at the most appropriate locations for its businesses and head office."
She added that Australia remained a key market, employing more than 6,000 of the bank's 13,600 staff.
The tax was announced in the May federal budget and is supported by both major political parties. It is expected to cost the sector a combined A$1.5 billion a year or A$6.2 billion ($4.6 billion) over four years in the planned budget. It has no sunset clause.
Analysts and investors said Macquarie's decision not to deny a potential move was likely political, but doubted it would shift its headquarters over a tax that, at six basis points on certain liabilities, would be minor and which it may not be able to escape in any case.
"I wouldn't have thought this tax alone would be enough to catalyse (a move) unless they are worried it could go up again in the future," said Shaw and Partners analyst David Spotswood.
"I just suspect it is signalling to the government and letting them know they are not happy and there are things they can do about it.
Foreign banks like Citigroup Inc (NYSE:C) C.N and HSBC Holdings PLC HSBA.L would still be subject to the Australian tax if their local liabilities reached A$100 billion, according to Australia's Treasury Department.
In warning of potential unintended and disproportionate consequences, Macquarie noted that international and wholesale businesses are run through its Australian arm but only one-third of the subsidiary's earnings are generated domestically. It did not elaborate on what those consequences might be.
Moving operations, particularly headquarters, is costly and complex for large institutions.
Rival HSBC HSBA.L last year dropped a proposal to shift its headquarters from London to Hong Kong, its main profit generating hub, after a 10-month review, triggered partly by Britain's tax on banks' global balance sheets that cost HSBC $1.1 billion in 2014. Analysts had estimated the cost of moving out of London at between $1.5 billion and $2.5 billion.
Karara Capital investment manager Rohan Walsh said Macquarie's business had been growing strongly internationally, particularly in the United States and Europe, and it could eventually make sense to move.
"Any consideration to move overseas will not be driven by the bank tax," he said. "It will be driven by the business mix." ($1 = 1.3532 Australian dollars)