I contacted Campbell's and complained about their 25% less sodium version containing the same amount of sodium than the regular and at a higher price. Of course, they justified the price increase but opted not to answer the 25% less sodium claim. Here's how they replied.

we received your message and appreciate your taking the time to contact Campbell Soup Company.
Currently, we offer three varieties of condensed Tomato soup with different recipes. They are: Campbell’s Tomato Soup, Campbell’s 25% Less Sodium’ Soup and Campbell’s Healthy Request Tomato Soup.

The 25% Less Sodium version costs more to produce because the recipe contains a number of different ingredients, we use different amounts of some ingredients and we make smaller quantities of the 25% Less Sodium variety. Retailers, of course, establish the price that consumers pay at their stores.

While these two products may seem similar (both contain 480 mg. of sodium), they have different recipes with slightly different ingredients, different quantities of some ingredient, all of which result in a different taste. The costs of ingredients and smaller-scale production for Campbell's 25% Less Sodium’ Tomato soup are higher than the regular Campbell's Tomato soup.

The 25% Less Sodium version costs more to produce because the recipe contains a number of different ingredients, we use different amounts of some ingredients and we make smaller quantities of the 25% Less Sodium variety.

Retailers, of course, establish the price that consumers pay at their stores.