The dockworkers’ strike, their first since 1977, could snarl supply chains and cause shortages and higher prices if it stretches on for more than a few weeks. Beginning after midnight, the workers walked picket lines Tuesday and carried signs calling for more money and a ban on automation that could cost workers their jobs.

President Joe Biden and his administration have signaled to both sides in the high-stakes dockworkers strike that they need to work things out “fairly and quickly,” the White House said in a statement Tuesday.