The plans will only be implemented if the company, a subsidiary of Wisconsin-based Alliant Energy Corp., is allowed to build a new $1.5 billion coal plant in Marshalltown.
The company expects to complete the regulatory application process and get an answer from the Iowa Utility Board this summer.
That plant, if regulators approve it and it's built as scheduled, is expected to be operational in 2013.
At that time two units at the Lansing Generation Station would be shut down and the Dubuque Generation Station would switch to natural gas.
Interstate Power and Light President Tom Aller said any changes in employment levels will be managed through retirements or attrition.
The changes would reduce carbon dioxide emissions by more than 800,000 tons a year, the company said in a statement.