A former Fort Worth City Council member is facing a second challenge seeking to keep her off the ballot in a November state Senate race.

GOP incumbent Kim Brimer requested an injunction Thursday to prevent Democrat Wendy Davis from appearing on the ballot. The filing in a Tarrant County court says that Ms. Davis did not resign from her council seat before filing for the Senate, which Mr. Brimer said should invalidate her place on the ballot.

The arguments are similar to ones made by a group of firefighters who filed a lawsuit against Ms. Davis in January. Those firefighters, who were backing Mr. Brimer, lost when the 2nd Court of Appeals ruled that they didn't have standing to file the suit. No court ruled on the substance of their arguments.

Matt Latham, campaign manager for Ms. Davis, called the court filing a desperate political trick. He said that Mr. Brimer is filing this suit now because of polls showing that his lead over Ms. Davis has narrowed.

"What takes him six months to file?" Mr. Latham said. "Absolutely nothing changed from New Year's Day to July 4. None of the facts changed."

Judd Pritchard, a spokesman for the Brimer campaign, said his boss isn't trying to avoid a tough campaign. He said that Mr. Brimer wants to ensure that his opponent is on the ballot legally.

"You want to make sure that it's not a race that ends up with a false start because you have a problem with one of the candidates," Mr. Pritchard said.

The suit was filed against Ms. Davis, Tarrant County Democratic chairman Steve Maxwell and state Democratic chairman Boyd Richie.

The portion of the Texas Constitution cited in the court filing says that no "person holding a lucrative office under the United States, or this State, or any foreign government shall during the term for which he is elected or appointed, be eligible to the Legislature."

One potential key to the debate over this passage is which word is missing but implied. Does eligible mean eligible to run for the Legislature or eligible to serve in the Legislature?

Both sides said that past state Supreme Court rulings and attorney general opinion have leaned in their favor.

However, this suit was filed just a few days after an Austin judge ruled on a case involving some similar issues.

Democrat Bill Dingus was still a Midland City Council member when he filed to run against incumbent Republican State Rep. Tom Craddick. Mr. Craddick, the House speaker, challenged his opponent in court and lost Monday when state District Judge Margaret Cooper ruled that Mr. Dingus was eligible to run for the House seat.

However, federal Judge Walter Smith ruled in April that Mr. Dingus was not eligible to appear on the ballot. "The Court agrees that a person holding a lucrative office, such as a member of the Midland City Council, is not eligible to become a candidate for the Texas Legislature," Judge Smith wrote.

Even with those issues up for debate, the Davis campaign is sticking to its original argument that she had resigned before she filed for the Senate seat and that officially happened when she was replaced by her successor.

Ms. Davis's replacement, Joel Burns, was sworn into office in a private ceremony before the Senate filing deadline and then sworn in again at a City Council meeting after the deadline. Fort Worth officials took no official stance on that issue.