SYDNEY: Traffic at Australia's ports could be crippled by as much as half as the nation's dock workers threaten a sweeping five-day strike over pay and working conditions, officials said Thursday. The Maritime Union of Australia has vowed a national walk-out from Saturday of 2,000 wharf staff if top freight company Patrick do not come back with a “serious offer” on wages and improved working conditions. Dock workers want a six percent pay rise, 13 percent pension contribution, a sign-on bonus and introduction of a safety officer for each shift following four deaths on the wharves in five years. They won permission to strike from the industrial tribunal earlier this year if the stalemate could not be resolved. Patrick, a subsidiary of the listed Asciano group, says the strike will bruise the economy as it tries to recover from massive flooding and cyclones and trade-exposed industries struggle with the surging Australian dollar. “The cumulative effect of the nationwide stoppages the union plans is 33 vessels ... that's approximately 35,000 containers,” a Patrick spokeswoman told the AAP newswire. “It will effectively shut down 50 percent of Australia's containerized freight capacity for a five-day period.” The MUA said it would consider exempting Brisbane port, gateway to the disaster-struck northeast, from the strike action in order to minimize disruption to recovery operations. “If there's a clear demonstration our action will affect Queensland, we'll discuss that with the Queensland government,” said MUA deputy national secretary Mick Doleman. Patrick has offered a four percent pay rise and said the strike decision, which follows seven months of talks, had come as a “bit of a shock”. But the spokeswoman said the union had effectively logged demands worth Aus$40 million (US$41.8 million) — a 30 percent increase on benefits currently received by workers — and the company “simply cannot agree”. The MUA and Patrick have a long history of clashes, the most famous of which — a seven-week waterfront strike of 1998 — was among the biggest industrial stand-offs in Australian history. — Agence France-Presse The action comes as national airline, Qantas, faces a walkout of some 9,000 pilots, engineers and ground staff, also over workplace contracts.