A strike involving port workers across the east coast impacted Port Tampa Bay Tuesday, when dozens of longshoremen walked off the job and onto the picket line.

The union representing U.S. dockworkers signaled that 45,000 members will walk off the job at midnight, kicking off a massive strike likely to shut down ports across the East and Gulf coasts

Ever since metal containers revolutionized shipping nearly 70 years ago, dockworkers have fought to defend the vital role they play in global commerce. Yet technological advances continue to threaten the role of manual labor in ports.

The 45,000 dockworkers who went on strike Tuesday for the first time in decades at 36 U.S. ports from Maine to Texas may wield the upper hand in their standoff with port operators over wages and the use of automation.