A coalition of Indiana tea party groups is planning a statewide convention this month that will culminate with them endorsing a candidate to run against Sen. Richard Lugar, an organizer said.

The tea party meeting is set for Sept. 24 in Greenfield, with those attending voting in a straw poll of Senate candidates for the 2012 Republican primary election.

Each preregistered tea party group in the state will be allowed to have two voting representatives at the meeting, said Monica Boyer of Warsaw, who is a tea party organizer and co-chairwoman of Hoosiers for Conservative Senate.

The Journal Gazette of Fort Wayne reported Wednesday that Boyer said Lugar hasn't responded to the group's questionnaire, while state Treasurer Richard Mourdock "has enthusiastically agreed to participate."

Nine representatives of Hoosiers for Conservative Senate — one from each of Indiana's congressional district — will decide on a candidate endorsement after the straw-poll vote.

Indiana tea party activists attending a January meeting signed a letter asking Lugar to not seek a seventh term.

Mourdock is the only other Republican who has entered the race against Lugar, and he has actively sought the backing of tea party supporters.

Rep. Joe Donnelly is the only announced Democratic candidate for the Senate seat that Lugar first won in 1976.

The Hoosiers for Conservative Senate group has criticized Lugar on issues such as his support for the Development, Relief and Education for Alien Minors, or DREAM,  Act, which would help some illegal immigrants who came to the U.S. as children obtain citizenship, and his votes in favor of President Barack Obama's Supreme Court nominations.