In the era of gentle parenting, even the word discipline can feel like a third-rail topic. It’s certainly foreboding when it’s first mentioned in Cristian Mungiu’s “Fjord,” the prickly Romanian Palme d’Or winner opening in theaters this weekend. It's built to get under your skin.

Sebastian Stan gets the honor of saying it first. The actor may have become famous for Marvel movies and American roles, but he draws on his Romanian roots and language skills to play Mihai Gheorghiu, a Romanian father of five. He also sheds some of his movie-star polish for the role, dressing frumpier and sporting a robust bald spot. He tells his new neighbors that discipline is how he and his wife, Lisbet ( Renate Reinsve ), manage so many kids, including two teenagers, two younger ones and an infant. The family, who are devout Christians, has just relocated from Romania to Norway. It’s where Lisbet is from, and where they’ll have family support.

This move, he says, was in the kids’ best interest. It’s an oft-repeated phrase throughout the movie — an innocuous, universal sentiment for any parent justifying their actions. But it starts to take on a different tenor when Child Protective Services launches an investigation into their family for suspected abuse.

Alarms are raised when one day their eldest daughter, Elia (Vanessa Ceban), shows up to the bus stop with a mark on her face and a bruise on her shoulder. Her brother Emmanuel (Jonathan Ciprian Breazu) says a few different things about why she has those marks, and one is that their mother punished her. As the audience, we know that there was a “punishment” the night prior after the older kids, in a rambunctious state of play, bumped into their mother who was holding hot liquid and fears she’s scalded the baby. But we don’t see what happens after.

The woman driving the bus, Frida (Lisa Loven Kongsli), who is also the child services liaison for the school, overhears the kids talking about the punishment and reports it. From there, things spiral quickly: The kids, who acknowledge some spankings, are almost immediately separated from their parents and placed with other families. Even the baby, who, Lisbet pleads, is still breastfeeding, is removed from the home and from their care. They're told these measures will last only the duration of the investigation and trials, but no one knows whether that will be a matter of days, weeks or even months.

What transpires is a moral battle between a progressive majority and a fundamentalist minority, that’s loosely inspired by a real story in which a Romanian father and Norwegian mother separated from their kids for some seven months.

The Gheorghius are a tight family unit — the first shots show them exchanging long hugs after some kind of disagreement we’re not privy to. We don’t really see them raise their voices at the kids. But Mihai concedes he has spanked them on occasion, which is not allowed in Norway and could result in possible imprisonment. But the trial seems to be about more than spanking: Their entire belief system seems to be fair game as the concerned Norwegians wonder why they don’t allow their kids access to modern things like phones and YouTube.

Mungiu, who is perhaps best known stateside for his anxious abortion drama “4 Months, 3 Weeks and 2 Days,” which also won the Palme d’Or, patiently plots out his slow burn drama which seems designed to tie your stomach in knots. Relief only comes through the serene shots of the landscape. With its robust runtime, plenty of little dramas unfold throughout the film — the older kids start to show some independence, spurred by their friendship with the neighbor’s rebellious daughter. The neighbor’s wife also helps defend them against a slick and obnoxious lawyer.

While Mungiu has said his film does not represent his views, “Fjord” seems to take a side in some ways, which defeats the point of the exercise, at least for the audience. Progressive extremism is certainly an interesting area to explore cinematically, but it’s difficult to shake the feeling that corporal punishment of children might be a needlessly provocative starting point for a culture war debate, at least the way “Fjord” handles it.

“Fjord,” a Neon release in theaters Friday, has not been rated by the Motion Picture Association. Running time: 146 minutes. Two and a half stars out of four.