Plano plans to hold a special election to fill the City Council seat of Mabrie Jackson, who resigned Monday to run for the state Legislature.

Council members originally were preparing to fill her seat by appointment, a power granted in the city's ordinances. But the state constitution requires Plano to hold a special election within 120 days.

Officials have not settled on an election date, though several leaders said the city is considering late January. The council will discuss plans at its next session, which is Monday.

"This is all new to us," Mayor Phil Dyer said. "The clock is now ticking."

Leaders had considered holding the vote during the March 2 primary to save on administrative costs.

Election rules, however, prohibit the city from having a special election within 30 days of a political primary. And given that the state requires an election take place within four months, a date toward the end of January is the latest the city can choose.

Plano has seen seats on the eight-member council come open in midterm before. In fact, it has happened five times this decade.

But in 2005, Plano voters chose to extend the terms of sitting council members – to three years from two. The longer terms triggered the state's special election requirement.

Ken Lambert was the last council member to leave early. He resigned to run for mayor in January 2006.

Calling a special election in that instance was not necessary: Voters chose Lambert's successor, Lee Dunlap, during a regularly scheduled council election that May.

Who might vie for Jackson's seat is unclear. Candidates must live in her district, which covers much of northern-central Plano.

Loretta Ellerbe, a former council member who lost her seat to Jackson last year, said she is considering a run.

Council colleagues, meanwhile, have set their sights on the challenges ahead.

"There's never a good time to lose a good person, obviously, with budget matters going and everything," Dyer said.

Jackson plans to run for the House District 66 seat held by state Rep. Brian McCall. He will not seek re-election.

City Council member Harry LaRosiliere, said the vacancy could not come at a more "tenuous time" for the city.

Plano must reconcile sizeable budget shortfalls in the next two years and faces stagnant housing and commercial growth.

The council, which wields broad authority over land use, the city's property tax rate and other matters, will dictate which direction Plano takes from here.

"We have some very important decisions to make," LaRosiliere said. "The learning curve is going to be pretty steep."