HOUSTON - About 45,000 port workers across the US East and Gulf Coasts went on strike Tuesday as a midnight deadline for a new labor deal over wages and automation had passed.

Labor negotiations stalled between the International Longshoremen's Association (ILA) and the United States Maritime Alliance (USMX), leading to the shut-down of up to 36 East and Gulf Coast ports.

The two sides, which had not been in formal negotiations since June, reportedly moved off their previous wage offers on Monday, but apparently no deal had been reached as picket lines went up from Port of Philadelphia to Port Houston in Texas, with striking dockworkers carrying signs reading "No Work Without a Fair Contract."

The USMX, which represents the ports, said in a statement on Monday evening that it requested an extension of the current contract and increased its offer by raising wages by nearly 50 percent over the life of the contract.

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The employer alliance pledged to keep the limits on automation in place from the old contract. But the labor union wants a complete ban on automation, according to an AP report.

A statement from the ILA said earlier on Monday that employers have refused to compensate workers fairly.

"The ILA is fighting for respect, appreciation and fairness in a world in which corporations are dead set on replacing hard-working people with automation," the ILA statement said. "Robots do not pay taxes and they do not spend money in their communities."

Local media reported that the ILA is seeking for a 77 percent wage increase over the six-year life of the contract, for the union workers to make up for inflation and years of small raises.

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The ILA members make a base salary of about 81,000 dollars per year, but some can pull in more than 200,000 dollars a year with large amounts of overtime, said the report.

The affected ports handle roughly half the country's cargo ships. Local experts estimate that the strike, the first of the ILA since 1977, could cost the US economy up to $5 billion a day, stirring inflation and supply chain concerns weeks before the presidential election. Some say it has the potential to become the most disruptive strike to the US economy in decades.