NEW YORK >> U.S. ports from Maine to Texas shut down this week when the union representing about 45,000 dockworkers went on strike for the first time since 1977.

Workers began walking picket lines early Tuesday near ports all along the East and Gulf coasts.

A shutdown that lasts more than a few weeks has the potential to raise prices and create shortages of goods throughout the country as the holiday shopping season — along with a tight presidential election — approaches.

There have been some signs of movement in the talks, with the U.S. Maritime Alliance, which represents ports and shipping companies, saying that both sides have moved from their initial wage offers. But on Wednesday, the alliance called on the International Longshoremen’s Union to come to the bargaining table. “We cannot agree to preconditions to return to bargaining, but we remain committed to bargaining in good faith,” the group said in a statement.

Late Wednesday night, the ILA said that Harold Daggett, its president, and other union officers, had received death threats since the strike began. The union said the threats were reported to police.

President Joe Biden told reporters Thursday that he thought progress was being made in ending the strike. Asked how much, Biden said “We’ll find out soon.”

What are the issues in the strike?

The union is demanding significantly higher wages and a total ban on the automation of cranes, gates and container-moving trucks that are used in the loading or unloading of freight at 36 U.S. ports. Those ports handle roughly half of the nations’ cargo from ships.

The contract between the ILA and the United States Maritime Alliance, which represents the ports, expired Tuesday.

The union’s opening demand was a 77% pay raise over the six-year life of the contract, with Daggett saying that it would make up for inflation and years of small raises. ILA members make a base salary of about $81,000 per year, but some can pull in over $200,000 annually with large amounts of overtime.

On Monday, before workers hit the picket lines, the alliance said it had increased its offer to 50% raises over six years, and it pledged to keep limits on automation in place from the old contract. The alliance also said its offer tripled employer contributions to retirement plans and strengthened health care options.

Which ports are affected?

While any port can handle any type of goods, some ports are specialized to handle goods for a particular industry. The ports affected by the shutdown include Baltimore and Brunswick, Georgia, the top two busiest auto ports; Philadelphia, which gives priority to fruits and vegetables; and New Orleans, which handles coffee, mainly from South America and Southeast Asia, various chemicals from Mexico and North Europe, and wood products from Asia and South America.

Other major ports affected include Boston; New York/New Jersey; Norfolk, Virginia; Wilmington, North Carolina; Charleston, South Carolina; Savannah, Georgia; Tampa, Florida; Mobile, Alabama; and Houston.

Can the government intervene?

If a strike were deemed a danger to U.S. economic health, President Joe Biden could, under the 1947 Taft-Hartley Act, seek a court order for an 80-day cooling-off period. This would suspend the strike.

But during an exchange with reporters on Sunday, Biden said “no” when asked if he planned to intervene.

“Because it’s collective bargaining, I don’t believe in Taft-Hartley,” Biden said.