The British Medical Association wants fatty foods to cost more in the hope it might convince people to eat more healthy foods.
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They're worried because people are getting fatter and fatter in the UK, and health problems to do with being overweight costs the health service about £500m every year.
But experts say a problem with this type of fat tax is the people who buy the most high-fat foods tend to be poorer families.
This means they would have less money to spend.
All other countries in Europe - except Ireland - already add some sort of tax to different kinds of food.
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