WPS Health Insurance has notified the state it will begin laying off about 450 employees at the end of March.
The layoffs are mainly because the company lost two major federal contracts.
The layoffs will start March 29 and affect workers at six locations -- one in Madison, four in Monona and one in Wausau.
The company said 250 people in Monona and Madison and 201 people in Wausau are affected.
The Monona-based nonprofit health insurer anticipates additional layoffs if it doesn't find new business to replace the federal contracts.
WPS CEO Mike Hamerlik said last November that up to 600 employees could lose their jobs in 2013. The company lost contracts to process Medicare claims as well as manage care claims for the military in 21 states.
The contracts made up about 40 percent of the company's annual revenue last year.
In a news release, Hamerlik says, "This is difficult for WPS and its employees, but is real and necessary and the company will focus on meeting the needs of customers."