Some 3,500 workers from mining giant BHP Billiton\'s Queensland coal mines began a seven-day strike on Wednesday in what unions said was one of the nation\'s largest industrial stoppages in a decade. The Construction, Forestry, Mining and Energy Union (CFMEU) said the strike affected seven mines in the Bowen Basin which have a normal weekly production of up to one million tonnes of coking coal, used to manufacture steel. \"Today is the first day of this current seven-day stoppage,\" CFMEU district president Stephen Smyth told AFP, adding that this was the first strike across BHP\'s seven mines in the coal-rich basin. It is also likely the largest industrial action in Australia since the maritime dispute of the 1990s, given the number of people involved, he added. BHP, which earlier this month posted one of the largest first-half profits in Australian corporate history -- US$9.94 billion -- is the world\'s biggest miner and one of the globe\'s largest producers of coal. Workers have been in dispute with BHP Billiton Mitsubishi Alliance (BMA) -- which operates the seven mines -- over conditions, including housing, safety and union representation, for more than a year. BHP would would not comment on the potential disruption to production. \"We\'re disappointed with any decision to stop work, but we remain committed to resuming negotiations in good faith. We just really want to get back to the negotiating table,\" a BHP spokeswoman told AFP. \"We reserve the right to manage our business safely and in a commercially successful way, and we\'re urging employees and representatives to return to constructive discussions.\" But the union said BHP was enjoying record profits at the expense of workers and needed to be more flexible in its negotiations. \"Last year, BHP made a record $23 billion profit. These workers are taking a stand for safe, secure jobs -- BHP can afford to do the right thing,\" CFMEU National President Tony Maher said. The three unions involved -- CFMEU, Australian Manufacturing Workers Union and the Communications, Electrical and Plumbing Union -- represent more than 3,000 workers at the seven coal mines owned jointly by BHP and Mitsubishi Corp. Queensland is a key global exporter of seaborne coking coal used in steelmaking.