VANCOUVER, B.C. (MarketWatch) — “Got Milk?” could be the battle cry for recent cross-border skirmishes that seem to originate around dairy cases and crowded parking lots just south of here at the U.S./Canada border.

So many Canadians have been buying cheaper milk just south of Vancouver in big-box shopping mecca Bellingham, Wash., that U.S. dairy convenience stores have been springing up — as well as snarky new Facebook pages asking Canadian grocery shoppers to stay home and buy milk, even if it’s twice as expensive.

Milk -seeking Canadians have even been called “milk piranhas” on the Facebook page. Talked about botched metaphors.

The big picture: Milk costs about $2.50 a gallon in the border town of Bellingham, Wash., where Costco is parked, about 40 miles south of this Canadian metropolis. In Vancouver, it’s twice that. I winced at paying C$2.50 for milk here this week, because it was for a half gallon, or two liters (Canada is totally metric).

But U.S. dairy farmers, Canadians point out, are subsidized , and Canada’s are not. Which largely — but not entirely — accounts for the sizable price disparity. In general, most groceries cost quite a bit more in Canada, where taxes — and government services — are much higher than in the U.S. Just try to find a box of cereal for under $4.50 here in a British Columbia grocery.

I should have seen this “battle” coming a few months ago, when a Seattlle TV station ran a story about Canadians flocking south to buy milk. The story had footage of a woman putting 19 (!) gallons of milk in her SUV at the Costco in Bellingham. That’s a lot of milk, but I’m guessing — nay, hoping — it was also for her family and/or neighbors.

Shortly after, the Bellingham Costco installed a vastly expanded refrigeration unit for milk.

Then there was the recent creation of a Facebook community page called “Bellingham Costco needs a special time just for Americans,” which attracted rude comments like, “It’s hard to find a parking spot. Them (sic) Canadians can be rude.” The page suggested earlier shopping hours just for local customers.

The head of the Bellingham/Whatcom Chamber of Commerce, Ken OIplinger, not wanting to kill his city’s golden retail goose, slammed the Facebook page, saying that if that naive suggestion about Costco having special opening hours for Americans were ever instituted, “If I were a Canadian, it would tell me I wasn’t welcome and I was a second-class shopper.”

“All those Canadians,” Oplinger reminded Bellingham residents, “Are paying taxes and helping our local government provide services.”

The Facebook page soon made amends, apologizing profusely to any Canadians who were offended, blaming the root problem at the local crowded Costco on the store not expanding more. It even referred, a bit mawkishly, to “beloved Canadians.”

As a rule, Canadian customs officials have tended to turn a blind eye to cars bringing back far more groceries than the C$20 or less allowed for a day shopping trip.

But American business opportunism has come to the rescue — before any milk is spilled:

A large upstate Washington company, Lynden, Wash., -based Edaleen Dairy, has set up a second “milk outlet store,” just across the border to take advantage of the strong Canadian dollar and the Canadians’ thirst for milk. The new store is in the border town of Sumas, Wash. — five minutes from the popular Abbotsford border crossing. Its two stores are selling milk as cheaply as Costco’s.

“We take Canadian money at par,” says an Edaleen exec — the Canuck loonie has been trading just above the greenback. “We have two cash drawers, one for U.S., one for Canadian. And we take Canadian debit cards.” (Personal note: You can get cash back in the U.S. with a Canadian debit card, but the reverse isn’t true, as we were reminded this week at a Vancouver Safeway when we tried to get cash back at the checkout after buying groceries.)

The two dairy outlet stores near the Canadian border certainly bring life to the old term, “Milk run.”

Sure sounds better than “run for the border.”