State Democrats have authorized the party to file a legal challenge to prevent Laura H. Thielen, a former director of the state Department of Land and Natural Resources under former Gov. Linda Lingle, from running for state Senate as a Democrat, sources say.

The party’s state central committee on Sunday chose to affirm an earlier decision that Thielen was not eligible to run for office under the party’s banner because she has not been a member in good standing for at least six months. Thielen had asked for an exception to the six-month rule, but was denied.

Thielen has filed to run in the primary for the Windward Senate seat now held by Sen. Pohai Ryan (D, Lanikai-Waimanalo).

“It seems unfortunate that a small group of people are giving the broader party membership a bad name,” Thielen said of the party’s state central committee. “And they should let voters decide.”

Democrats at the party’s state convention last weekend agreed to modify the rule and allow potential candidates who have not been party members for six months to interview with party leaders and demonstrate their fidelity to the party’s platform. Some Democrats believed the rule change would provide a reason for the party not to legally challenge Thielen’s candidacy.