Did you catch this ad on the back of Baylife Magazine on Sunday? (If you did, first of all, thanks for finding it. The thing was buried inside my newspaper like a tick. Almost needed a sizzling match head to burn it out.)

I looked at the ad yesterday and thought, “Well, that’s something you don’t see every day; a soup company running smack.”

Turns out it was a return salvo fired back at Campbell’s for an ad that company ran in late September accusing Progresso of containing the three dirtiest letters in the alphabet: MSG.

BrandWeek magazine wrote about the opening shot a few weeks back:

In a category not known for vitriol, Campbell has launched an ad taking direct aim at its rival, General Mills’ Progresso. An ad in today’s New York Times shows a can of Progresso with the caption, “Made With MSG.” Opposite the page is a picture of Campbell’s Select Harvest with the headline: “Made With TLC,” for Campbell’s new, natural-ingredients soups. The MSG in this case refers to monosodium glutamate while TLC stands for “tender love and care.” BBDO, New York, handles.

Why the salvo? General Mills’ Progresso Light soups were a big hit in 2007, in part because of a Weight Watchers endorsement that gave the line a zero-point rating (that’s good). The Minneapolis-based cereal maker introduced the soups in nine new Light varieties last month. Now, at the beginning of soup season, Campbell is on the attack.

“You have to give Campbell credit for taking advantage of the good, clean ingredients statement that they have on their soups,” said Lynn Dornblaser, new products expert at Mintel, Chicago. “It’s a very smart move to take that and [contrast] it to the MSG comparison.”

So far, Progresso hasn’t taken the bait. Recent ads by Saatchi & Saatchi, New York, show Progresso trying to go after the male soup consumer. One ad shows a man eating soup in the kitchen while his wife watches. “Eating light?” the wife asks. “Light? No. Look at this. Big chunks of chicken, vegetables and pasta,” he replies. The spots reinforce the fact that soup can be light and filling. Tagline: “Progresso. What a light soup should be.”

BrandWeek followed up that story with another article on Oct. 8 after the Progresso ad ran in the New York Times:

The full-page ad for Progresso, also in The New York Times, refutes Campbell’s assertion that its soups are made with TLC or “tender love and care” and all-natural ingredients, while Progresso’s are made with MSG, a food ingredient known as monosodium glutamate. The ad reads in large red letters: “Campbell’s has 95 soups made with MSG.”

The ad follows Progresso’s announcement today that it has removed the food additive from 26 of its soups. General Mills had originally planned on disclosing the strategy after the remaining 50 soups were reformulated to exclude MSG, but Campbell’s ran the ad.

“Campbell fired the first shot and Progresso has responded with missiles,” said Julia Beardwood, a principal at brand consultancy Beardwood & Co., New York.

To back up its claim, the Progresso ad shows what looks to be close to 95 soup cans—all lined up in several rows. The Campbell ad that ran three weeks ago showed a smaller, 19-oz. can of Progresso Traditional Chicken Noodle against a slightly taller can of Campbell’s Select Harvest Chicken with Egg Noodle, in order to compare contents of the two soup brands.

“How did we do it? We went to store shelves, bought their soups, read their ingredient labels and added up the number of Campbell’s soups that contain MSG and that was a big number,” said General Mills rep Tom Forsythe.

First thought: Male soup consumers? There are enough to consider that a batch? I mean, I love soup as much as the next X and Y chromosome carrier. I had no idea I was being targeted in such a way.

Second thought: God help us if this turns into an East Coast v. West Coast rap-style battle. Next thing you know, someone will bust a cap in Lipton and Manischewitz outside the Vibe awards.