JEFFERSON CITY, Mo. -- Environmentalists are proposing a ballot initiative that would force electric utilities in Missouri to make greater use of renewable energy.

The group Missourians for Clean and Safe Energy has submitted five versions of a potential initiative to the secretary of state's office.

The most far-reaching proposal would apply to all investor-owned utilities, electric cooperatives or municipal utilities serving more than 25,000 customers. It would require that at least 20 percent of their electricity come from renewable sources such as wind or solar power by 2021.

The most limited proposal would apply only to investor-owned utilities and mandate that 11 percent of their electricity come from renewable sources by 2020.

Each of the versions would impose a 1 percent limit on the average retail price increase attributable to the renewable energy.

Campaign spokesman P.J. Wilson said Thursday that the group has not decided which version to pursue. He also declined to identify who was financing the effort. The initiative was announced in a news release from the St. Louis-based Great Rivers Environmental Law Center.

Last year, Missouri enacted a law encouraging -- but not requiring -- investor-owned utilities to use renewable energy sources for 4 percent of their electric sales by 2012 and 11 percent by 2020. The Republican-led legislature intentionally avoided imposing a mandate.

But Wilson said that without a requirement, Missouri's new law "has absolutely no effect." What's necessary, he said, is either "positive incentives for utilities to comply or negative repercussions if they don't comply."

Wilson said supporters were prepared to use paid petition gatherers if Secretary of State Robin Carnahan's office clears them to begin circulating the initiative. To make the November ballot, the initiative would need signatures from at least 5 percent of the number of people who voted in the 2004 governor's race in at least two-thirds of Missouri's congressional districts.

In November 2004, Columbia voters approved an initiative to require that city to derive 2 percent of its electricity from renewable sources by the end of 2007; 5 percent by 2012; 10 percent by 2017 and 15 percent by 2022.