* Strike would hit over half of world platinum output
* Union members have already voted for Implats strike
* AMCU president says union is working-class "vanguard"
By Ed Stoddard and Zandi Shabalala
JOHANNESBURG, Jan 15 (Reuters) - South Africa's Association of Mineworkers and Construction Union (AMCU) said on Wednesday it would call a strike in the platinum industry if its members backed such action.
AMCU members have voted in favour of a stoppage at Impala Platinum over wages, and the union will canvas its rank and file this week at Anglo American Platinum and Lonmin.
The three are the world's top producers of the precious metal and account for more than half of global output.
A simultaneous stoppage at the trio would hit a key South African export at a time when the rand currency is near five-year lows and deal a fresh blow to investor confidence in the continent's biggest economy.
Renewed labour unrest will also be an unwelcome distraction for President Jacob Zuma and his ruling African National Congress ahead of general elections expected in three months.
AMCU President Joseph Mathunjwa told reporters a decision would be made next week.
"Yes, there will be a strike, if our members give us the go-ahead we won't hesitate to do that. AMCU is not a company, it doesn't have a board of directors. We get a mandate from our members," he said.
At Amplats and Lonmin, the union is seeking a minimum monthly wage of 12,500 rand ($1,200) for entry-level workers - more than double current levels, under the populist battle cry of a "living wage". At Implats the union scaled back its demand late last year to just over 8,500 rand.
Using typically combative language, Mathunjwa, clad in a trademark green AMCU shirt, said his union's drive for a living wage "has unsettled the capitalists, who have over the years benefited from intensified exploitation of workers".
Mathunjwa, a charismatic lay-preacher who has cast himself in the role of a Christian soldier fighting for South Africa's black workers, said AMCU was the "genuine vanguard of the working class" - wording sure to raise boardroom eyebrows.
AMCU has emerged as the dominant union on South Africa's platinum belt over the past two years after wresting tens of thousands of members from the National Union of Mineworkers (NUM) in a turf war in which dozens of people were killed.
This included the police killing of 34 striking workers outside Lonmin's Marikana mine in August 2012, the deadliest security incident since the end of apartheid which has become a political nightmare for the ANC on the platinum belt.
Companies have said they can ill afford steep increases as power and other costs soar against the backdrop of depressed prices for the white metal used in emissions-capping catalytic converters in automobiles.
Amplats, a unit of global mining house Anglo American , fell into a loss in 2012 in part because of a wave of wildcat strikes rooted in the NUM/AMCU conflict.
Platinum's spot price shed 11 percent last year and is about 40 percent down from record peaks scaled in 2008.
Mathunjwa on Wednesday also dismissed local media reports of divisions emerging in AMCU's ranks because some workers were reportedly angry at its failure to deliver on promises.
"There are no cracks in AMCU," he told Reuters.
He also said an AMCU chairman at Amplats, who was quoted in the Business Report newspaper as saying workers were losing patience with Mathunjwa, was a troublemaker who had been expelled from the union by the local branch.
AMCU also has thousands of members in the gold sector who have rejected wage increases of 8 percent agreed last year by NUM. Mathunjwa said its members could down tools at bullion producers such as AngloGold Ashanti.