Chris Smalls has all the makings of a hero. Young, charismatic and sympathetically rebellious, he quits his job at a New York Amazon warehouse over inadequate PPE provision, but doesn’t walk away: Instead, he launches an effort to establish a labor union at his former workplace, eager to improve conditions for those staying the course. It would be easy to build a halo-lit documentary portrait around this handsome, rabble-rousing father of three, but Brett Story and Stephen Maing’s excellent “Union” is something more finely shaded and community-minded than that. As a long-view anatomy of a unionization campaign, the film may be galvanized by Smalls’ presence at its center, but it’s rather less idealistic about the human politics involved in fighting corporations. Strong personalities inspire but they also divide; keeping everyone on side against a faceless foe is harder than Hollywood makes it look.

“Union” is no Hollywood film, though it underlines the nonsense of distinguishing documentary from “narrative” cinema. Plunging into the quest of Smalls and his Amazon Labor Union cohorts with no talking-head interviews or directorial commentary, and scant onscreen text, the film is all narrative, procedurally tracking the ALU’s circuitous rise in tensely linear fashion, alert to both the systemic obstacles and personal conflicts that keep snarling up their progress. This is an unexpectedly straightforward approach from Story, best known for such essayistic docs as “The Hottest August,” but the film has idiosyncratic vibrancy aplenty as a real-world character study — given cinematic vigor and texture by Maing’s expert lensing and cutting.

The film opens on some of its most arresting images — a montage of transportation modes at vastly different scales that neatly symbolizes Amazon’s dizzying economic hierarchy. Slowly and serenely, an enormous cargo ship enters into port, stacked with containers soon to be unpacked and processed in JFK8, Amazon’s sprawling “fulfillment center” (the irony needs no underlining) in Staten Island. Cut to the workers about to do that processing, cramming themselves into small, tardy transit buses early in the morning, like so much human cargo; cut again to the July 2021 launch of the Blue Origin NS-16 rocket into sub-orbital space, with Amazon CEO Jeff Bezos among its vanity crew members. Story and Maing take as given the gutter-to-stars distance between the working-class laborers powering the corporation and the detached billionaires at its helm; “Union” cares little for specific economic analysis, instead foregrounding the everyday desperation of those in the former camp.

As the working day closes, Smalls sets up a stand across the street and fires up a grill, serving up burgers and hot dogs to coax hungry departing workers into signing a labor union petition. (If they don’t want to sign, they’re still welcome to food — ultimatums and trade-offs are for the bosses.) He’s amassed a small crew of like-minded JFK8 employees, and they’re gradually getting through to co-workers weary of 11-hour workdays, meager breaks and any number of other exploitative indignities. Amazon fights back with fearmongering anti-union propaganda videos in the workplace, stressing the alleged security and stability of the status quo — despite an unmentioned worker turnover rate of 150%. Despite such efforts, the ALU mission gains ground, as they organize phone banks and bait converts with free marijuana, and inch toward the magic number of signatures (30% of the JFK8 workforce) required to trigger an election.

Often gathering on Zoom, the ALU begins as a bullishly unified group of self-described “comrades” — or “the NWA of the organizing world,” as Smalls, a former rapper, likes to say. Their members range from Maddie, a young, white, comparatively privileged college graduate who hasn’t been able to parlay her degree into related employment; to Natalie, a toughened Latina who has been living out of her car for years; to anxious transit coordinator Jason, who initially finds in the union effort a sense of belonging that doesn’t come easily to him, but who needs more individual emotional support than his peers can provide.

The more roadblocks Amazon tosses their way, the more their collective sense of purpose weakens, not helped by Smalls’ brashly assertive leadership style, which isn’t always sensitive to the demands of those still working at JFK8. The gradually widening rift between him and Natalie, who would increasingly rather forgo their own campaign and wait for a national union to ally with them, is closely and compellingly mapped, and the film’s sympathies feel evenly split between them.

Smalls remains the documentary’s focal point, only growing more interesting as his personal and strategic flaws are exposed — it hardly seems possible to remain an unambiguous hero in the face of such wearying institutional machine, not to mention so many human nerves fraying at different paces. But there’s an admirably doughty resilience to the way he pushes through the election campaign regardless, toward an outcome in which even numerical victory can’t guarantee any concession from the enemy. At its close, as “Union” notes the variably rippling impact of the ALU’s efforts on other Amazon sites across America, its elegant observational approach veers into overt editorializing. But even the film’s most rousing takeaway is dimmed by a daunting awareness of scale, as the cargo ship slides back into port, and disempowered thousands — without the time, energy or money to fight another battle — trudge back to work.