A class-action lawsuit about overtime pay for truck drivers hinged entirely on a debate that has bitterly divided friends, families and foes: The dreaded — or totally necessary — Oxford comma, perhaps the most polarizing of punctuation marks.

What ensued in the United States Court of Appeals for the First Circuit, and in a 29-page court decision handed down on Monday, was an exercise in high-stakes grammar pedantry that could cost a dairy company in Portland, Me., an estimated $10 million.

In 2014, three truck drivers sued Oakhurst Dairy, seeking more than four years’ worth of overtime pay that they had been denied. Maine law requires workers to be paid 1.5 times their normal rate for each hour worked after 40 hours, but it carves out some exemptions.

A quick punctuation lesson before we proceed: In a list of three or more items — like “beans, potatoes and rice” — some people would put a comma after potatoes, and some would leave it out. A lot of people feel very, very strongly about it.