By some measures, delivering packages is one of the few “good” jobs left in America for people without college degrees. The Teamsters represents roughly 260,000 UPS workers, who make around $36 an hour, and the American Postal Workers Union represents around 156,000 mail carriers, who make, on average, $75,500 annually, according to the union.

Yet these union jobs are under pressure. “These are good jobs, and they can get much worse really fast,” Steve Viscelli, a sociologist at the University of Pennsylvania who writes about the trucking industry, told me. The Teamsters recently gave workers the go-ahead to call a strike amid ongoing contract negotiations, although the two sides said late last week they’d reached a tentative deal. The American Postal Workers Union is about to begin contract negotiations too. Workers are pushing back over weekend deliveries and the lower pay and benefits given to part-time workers. UPS now has a second tier of part-time workers who make as little as $10 an hour; the Postal Service has added workers it calls City Carrier Assistants who make less than regular mail carriers.

And then, of course, there’s Flex. If the delivery workforce continues to shift toward non-unionized workers and independent contractors, the industry could go from one where workers can support a family to one where they are making less than minimum wage. That’s what happened in the long-haul trucking industry, according to Viscelli. The average long-haul trucker today makes about $40,000, down from the equivalent of $100,000 in 1980.