NEW YORK — Anyone who has seen ‘‘On the Waterfront’’ knows East Coast longshoremen can be a tough bunch.

The dockworkers are flexing their muscles again, threatening a strike beginning Sunday that would shut seaports from Massachusetts to Texas. It would be the first such coastwide strike since a two-month walkout in 1977 paralyzed the flow of tens of billions of dollars of imports — and the nation’s retailers and other businesses fear a painful replay if the 14,500 dockworkers make good on their threats.