Strike or lockout: What's the difference?

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Container ships sit docked in a berth at the Port of Oakland on Feb. 17, 2015.

With fruit rotting dockside and automakers running out of parts, the West Coast port slowdown is starting to get costly.

The months-long labor dispute has stranded dozens of ships parked at sea waiting to unload, costing tens of millions of dollars in lost business. Some companies are scrambling to reroute shipments through ports that haven't been hit by the slowdown. But that often costs more.

Read More Who's at risk in the L.A. port slowdown

Even if the shippers and dockworkers union reach an agreement soon, it will take months to work through the backlog of unshipped goods.

Despite ongoing talks, the sides appear to be far from a settlement. They can't even agree on whether the slowdown is the result of a lockout by shippers or a work slowdown or partial strike by dockworkers.

Strike, lockout ... what's the difference?

For the farmers losing valuable crops or retailers unable to restock goods, it may not matter much. But the laws governing collective bargaining view the two actions very differently.

A strike happens when workers decide, as a group, to walk off the job to win concessions or terms from their employer. But there are rules governing when a strike is illegal.

Some labor contracts ban them; in some states, some public employees aren't allowed to strike. There are some exceptions to this rule, according to the National Labor Relations Board. If you walk off the job because of hazardous work conditions, for example, that may not violate a "no strike" provision.

The law also takes into consideration why you're striking. If you're demanding higher wages, or better hours or other changes in working conditions, you're considered an "economic striker." Workers who are protesting unfair labor practice fall into a second category.

The difference comes into play when the strike ends: unfair labor practice strikers have a stronger claim to getting their jobs back than economic strikers, according to the NLRB.

So what's a lockout?

In a lockout, management decides when employees stop working, sometimes by physically barring them from their jobs. In some cases, the employer is allowed to hire replacement workers to keep the business running.

At that point, the legal battle usually turns on whether locked-out workers are entitled to get their jobs back—with or without back pay—once the dispute is resolved. A lot depends on whether workers struck first and whether any strike or slowdown was considered illegal.

One of the most famous lockouts involved the 1981 firing of more than 11,000 striking air traffic controllers who defied an order by President Ronald Reagan to get back to work. In addition to losing their jobs, they were "banned for life" from working for the FAA. (The ban was later rescinded by the Clinton administration, which re-hired about 800 of the fired controllers.)

How often does this happen?

A lot less than it used to, according to Labor Dept data. Until the early 1980s, there were hundreds of work stoppages every year involving millions of workers. In the past decade, there have been an average of fewer than two dozen stoppages a year.

Some of the highest-profile labor actions have involved sports leagues, including baseball and football. But the economic impact of the port strike, if it goes on much longer, could be much more widespread.

So how long can the West Coast dockworker and shippers keep this up?

A federal mediator is already trying to get the two sides to come to terms. At some point, when a strike threatens to inflict wider economic damage or public harm, the law allows the president to go to court and try to get an injunction to stop the work stoppage.

Under the Taft-Hartley Act, the attorney general has to get a judge to grant the injunction. And to make the case, he has to show that the work stoppage threatens to "imperil the national health or safety" and that it "affects an entire industry or a substantial part thereof engaged in trade, commerce, transportation, transmission or communication among the several states or with foreign nations, or engaged in the production of goods for commerce."

It's not clear whether the current port slowdown meets that legal test. But there's a recent precedent. The last time a labor dispute at West Coast ports led to a shutdown in 2002, President George W. Bush used the Taft-Hartley to get an injunction to end a 10-day lockout.

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