By rule, (WAC 480-100-238) and (WAC 480-90-238), all natural gas and electric utilities regulated by the commission are required to develop plans for how they will obtain future energy resources for their customers. An Integrated Resource Plan is used to identify a utility company's long-term energy resource strategy. These plans describe how the company will meet future customer needs at the least cost to ratepayers. Utility companies are required to update their plans every two years.
The UTC completed a review of its rules for least cost plans in 2006.