One union — the Laborers' International Union of North America — called the move gutless, and accused the government of announcing it on a holiday weekend in the hope fewer people would be paying attention.
One member of that union says his phone is ringing off the hook.
Ron Berringer says he has received more than 30 calls since Friday, when the U.S. State Department announced Keystone XL would be delayed indefinitely. A presidential permit is on hold, apparently until next year at the earliest.
Union members are calling to ask what the move might mean for their livelihoods — and Berringer cringes whenever the phone rings.
"When they call, I almost dread even picking it up," said Berringer, a semi-nomadic construction worker from Iowa and shop steward for his Nebraska-based union local.
"I know what they're gonna talk about, and I know what I've got to tell them. And what I've got to tell them is, 'I just don't know.'"
Berringer is among the thousands of workers who will build the rest of Keystone XL, if it ever gets approval.
Their role has become central to the debate, with pipeline proponents arguing it would create thousands of construction jobs. Opponents, however, insist it would only result in a few dozen permanent jobs once completed.
The pipeline hardly seems like a macroeconomic game-changer in Nebraska, which has the third-lowest unemployment rate in the country at just 3.7 per cent. Even President Barack Obama has played down the project's potential jobs impact, calling the claims of its proponents overblown.
Berringer, however, insisted the project would make a difference in thousands of lives.
Construction is an unpredictable business, and pipelines mean guaranteed income for an entire season, he said — not to mention tens of thousands of dollars in overtime pay, weekend bonuses and per diems as crews work extra-long hours in an attempt to get the bitumen flowing by winter.
Berringer is growing frustrated with having to tell his fellow workers year after year that the pipeline isn't happening.
"They tell me, 'Well, how am I gonna make house payments and car payments and stuff?' And I felt sad for them, because I don't have an answer for that," he said.
"There's a lot of Laborers who would've made sure they were able to pay all their bills. They could've got their head above water. Now their head's gonna go below water."
The Obama administration has cited the uncertainty in Nebraska, where the pipeline's proposed route is currently the subject of litigation, as the reason it can't make a decision on the pipeline for now.
Nearly one-quarter of landowners in that state are refusing to sign easement deals with Calgary-based pipeline builder TransCanada Corp., and they're in court fighting a law that would have forced them to open up their property.
Berringer generally comes across as a pretty mild-mannered guy. But when asked to assess what's happened, he emits a couple of curse words about what he considers the bovine-fertilizer political theatrics surrounding the debate.
His brother Jason is in a similar spot. He'll be busy the next four weeks, helping to repair a Nebraska City power plant. Then he'll add his name to a list of union members looking for their next job, hoping something comes up by summer.
"It's not good," Jason said.
"I wish these (pipeline opponents) would get online and actually look and see what it costs them in the end, whether putting it though Nebraska or buying it from a foreign country. I know Canada's a foreign country, but they're our neighbours, too."
Jane Kleeb, an anti-pipeline activist in Nebraska, said a lot more jobs are at stake as Republicans in Congress block infrastructure spending. A budget proposal currently before the House of Representatives would strip $52 billion in spending on roads and infrastructure.
Kleeb is urging all sides of the Keystone debate to get together to press Congress to increase infrastructure spending.
As for pipeline workers, Kleeb said there are currently so many jobs in the sector that the Nebraska Laborers union has to bring in out-of-state employees, like the Iowa-based Berringers.
"We know that pipe welders are in very short supply," Kleeb said. "From what we understand, there is no huge lack of jobs like the Laborers have tried to portray."