ST. PAUL — Minnesota police officers and firefighters are retiring in greater numbers, apparently because of changes in the state pension rules that will take effect in July.

About 300 officers and firefighters retire each year, but for the fiscal year ending June 30 there will be an estimated 600 retirements, according to Public Employees Retirement Association of Minnesota. The group says the higher numbers reflect an increase in people who are moving up their retirement plans.

The state’s official retirement age for police and firefighters is 55, although they can retire as early as age 50 with a financial penalty for each early year. Under the new law, though, people retiring after June 30 will see the financial penalty for early retirement rise from 1.2 percent per year to 5 percent per year for most members.

That change has contributed to waves of retirements, which could lead to staffing shortages at police departments across the state. For example, 27 Minneapolis officers retired this month, or about as many as retire in an average year.

A cadet class of 32 inexperienced officers won’t be ready to begin field training until around Labor Day, the Minneapolis Star Tribune reported.