There’s plenty of time for the two sides to work out a deal. UPS employees can’t go on strike until their current labor contract ends on July 31. But the scars of the labor action 21 years ago are still fresh enough that businesses are paying close attention to the talks.

The walkout on Aug. 4 1997 led to hundreds of millions of dollars in losses for UPS. It was, at the time, one of the biggest nationwide strikes the country had ever seen.

It was a different time, though. The strike impacted consumers differently than it would today, since business owners saw the most direct effects, often unable to restock shelves.

Today, however, the UPS truck is a regular sight in residential neighborhoods, delivering packages from Amazon and other online retailers. And consumers are used to prompt delivery of those orders.

That puts one of the chief advantages union leaders had on their side in 1997 at risk. Public opinion, at the time, was strongly on the drivers’ side. A Gallup poll showed Americans favored striking workers over the company by a 55% to 27% margin.

It’s not guaranteed support would be that widespread today, which could put pressure on union leaders.

There’s another wild card at play that could impact a possible work action at UPS: Donald Trump.

Amazon’s tight relationship with UPS is supplemented by one with the U.S. Postal Service. Should UPS be unable to deliver customer packages, it’s possible the retailer will lean heavier on the USPS.

Trump, though, is no fan of that relationship, attacking Amazon in a series of tweets earlier this year, saying the company wasn’t paying enough to ship packages. Experts have disputed this position, saying Amazon and other online retailers have helped stanch the post office’s declining cashflow.

Still, a weakened Amazon could bring another round of Trump attacks. Or, worse, inaction.

President Bill Clinton refused to stop the 1997 strike, even though he did have the legal power to do so under the Taft-Hartley Act. But Labor Secretary Alexis Herman strongly urged the two sides to stay at the negotiating table for 80 hours of talks in a five-day period. That pressure is credited as one of the reasons the strike didn’t last longer.

Would Trump instruct Secretary of Labor R. Alexander Acosta to do the same, if doing so also helped Amazon? That’s unknown.

UPS, of course, is downplaying talk of a work stoppage.

“UPS is confident in our ability to reach an agreement that meets the needs of our employees and the business,” said UPS spokesman Glenn Zaccara, adding that the company and Teamsters have reached tentative agreements on a number of non-economic issues already.

Nonetheless, the mere threat of another widespread UPS strike is causing agita in boardrooms across the country.