A Canadian flight was cancelled and police were called because a child was not wearing a mask.
Safwan Choudhry says WestJet wanted his 19-month-old to wear a mask, but the baby girl would not stop crying.
The airline says the issue was not with the infant, who is below the age required to wear a mask, but with Mr Choudhry's three-year-old.
Tuesday morning's Flight 652 from Calgary to Toronto was stopped, and all passengers were ordered to disembark.
"It's unlike anything I have ever witnessed, let alone experienced," Mr Choudhry told the BBC.
Mr Choudhry told the BBC his oldest daughter, who is three, was eating a snack before take-off when flight attendants approached them asking that both their children wear a mask. He said he and his wife were masked.
He said he asked if his daughter could finish her snack, but that they said they had a "zero tolerance policy" and would not close the plane door without her wearing a mask. Mr Choudhry said he agreed to put one on immediately.
"Most children you have to kind of ease them into it, which is a code word for let me get the iPad out," he told the BBC.
He says the three-year-old did put on a mask, after some fussing.
"But my younger one had a very difficult time, she was basically hysterical."
Mr Choudhry says she was so upset she vomited.
He says WestJet was aggressive, and told them that because his youngest daughter was not wearing a mask, and was too upset to wear a mask, the whole family would have to leave.
He says they told them that if they did not leave, they could be arrested, charged and receive prison time.
Mr Choudhry says he and his wife were respectful. They ultimately agreed to leave.
He later learned that according to Canadian transportation policy, only children over two are required to wear a mask, and thus his 19-month-old did not have to put one on.
What does WestJet say?
WestJet disputes that the three-year-old put a mask on.
The airline said in a statement: "Due to non-compliance of the parents to place a mask on their older child who is over the age of two, our crew informed the adults of the regulations we are required to follow.
"Our crew requested the presence of the authorities after the guests refused to comply with Transport Canada's interim order and subsequently refused to deplane the aircraft."
A video taken with Mr Choudhry's phone shows his older daughter wearing a mask on the plane, after police arrived on board.
He says while some passengers were very irritated with his family, "overwhelmingly" people on the plane supported them. Many spoke up in defence of the family, as their youngest cried, he says.
That was when flight staff called police, he says. They got off the plane, and the flight was eventually cancelled and rebooked for the next day.
"Due to the rapid escalation of the situation on board, our crew felt uncomfortable to operate and the flight was subsequently cancelled," WestJet said.
In a video, a police officer explains to them that while the mask issue with the eldest was "resolved", "the behaviour of the other passengers left the rest of the crew feeling unsafe".
Some passengers can be heard in video of the incident heckling the police and air crew.
The officer later confirms that when he arrived, the oldest child was wearing a mask.
Police did not file any charges.
A fellow passenger, Marian Nur, also recorded some of the interactions with flight staff, because she was worried the family was being targeted because of their race and religion - Mr Choudhry's wife wears a hijab.
"I was so shocked, the parents never raised their voices, they never got angry with the attendants, they were just trying to reason with them," she told CBC.
Mr Choudhry says he and his family are still in Calgary, and have not been offered another flight to Toronto. He says he hopes this does not happen to anyone else.
"So many people were put through so much grief because of a lack-of-understanding on part of the policy," he says.