MADISON, Wis. -- Big-name propane companies are feeling the heat.

A class-action lawsuit alleges the companies have been misleading consumers by reducing the amount of product without changing the tank size.

Wisconsin's Consumer Protection agency said it's perfectly legal to lower the levels -- putting 15 pounds of gas in a 20-pound tank -- as long as there's a label clearly stating the amount in the tank.

"It's like sometimes we buy things in the grocery store, where if you look the box size looks pretty much the same as it used to, but it's actually a little smaller or it contains a little less," said Janet Jenkins, spokesperson for the Wisconsin Department of Ag, Trade and Consumer Protection.

"People have sold a number of products, or variety of products that look like they're in the same packaging but actually contain a little less, or a little smaller. So consumers don't know right off the top that they're actually paying the same price," said Jenkins.

Jenkins also said if consumers see tanks that don't display the weight of the product, to point it out to the retailer and contact Wisconsin's consumer protection agency.

The propane companies named in the lawsuit said they cut the fuel to cut their gas expenses last summer.

The suit names FerrellGas, which sells propane under the Blue Rhino brand. AmeriGas is also named.