The question of who will represent the Fourth District in the New Jersey General Assembly has taken another twist.

The state Supreme Court ruled Tuesday that Assemblywoman-elect Gabriela Mosquera cannot take office until questions surrounding the constitutionality of the state's residency requirements for elected officials are resolved.

The decision, which reversed an appellate court ruling on Monday, came shortly before noon, when the freshman Democrat was to have been sworn in with the rest of the Legislature.

William Tambussi, Mosquera's attorney, said his client was disappointed and would continue to fight in court.

"It's like Sunday the Broncos won with Tebow as quarterback and then Monday they find out the Steelers won on a technicality," he said.

Republican Shelley Lovett, a losing candidate in the Fourth District race, filed suit last month arguing that Mosquera had not lived in the district for a full year before the election, as required under the state constitution.

Mosquera, an aide to Gloucester Township Mayor David Mayer, moved to the township's Blackwood section in December 2010.

The residency provision had not been enforced by the New Jersey Attorney General's Office since a federal District Judge declared it a violation of the U.S. Constitution in 2002. But a decade of legal oblivion was overturned last week when Superior Court Judge George S. Leone declared that ruling incorrect and voided Mosquera's election.

The Supreme Court's decision on Tuesday followed advice by the New Jersey Attorney General's Office that, were Mosquera to be seated before the residency issue was resolved, the courts could lose the ability to decide her fate.

The announcement came so late that Mosquera's name appeared on the electronic board in the General Assembly chambers where votes are recorded.

"The people of the Fourth District elected Gabriela Mosquera because of her devotion to public service," Assembly Speaker Sheila Oliver (D., Essex) said in a statement Tuesday. "Let's get past the legal squabbles and respect the will of the voters."

It is unclear when the state Supreme Court will address the larger question of whether the residency rule is constitutional and, if it is, whether it should apply to Mosquera, who had been under the impression it was not an issue.

Residency requirements for elected officials have long been a point of judicial debate, said Edward Hartnett, a constitutional law professor at Seton Hall University.

Rules vary from state to state concerning how long a candidate must have resided in a district, Hartnett said. "There's a lot of different ways to look at this," he said.

The immediate question is what will happen to what was presumed to be Mosquera's seat.

Last week, Leone ordered Democrats to appoint an interim Assembly member for the district, which includes portions of Camden and Gloucester Counties, by Feb. 14. The Supreme Court affirmed Leone's order, but Tambussi - who also represents the Camden County Democratic Committee - questioned whether the party was still legally bound to name a fill-in.

"It's uncertain given the court rulings," he said.

Lovett's attorney, Matthew Wolf, said he planned to appeal Leone's ruling, arguing that the Republicans who should appoint an interim Assembly member.

Republican Domenick DiCicco Jr. represented the Fourth District in the Assembly until its boundaries were redrawn. Since Mosquera's bid to replace him was invalidated, Wolf argued, the GOP last legitimately held the seat and should decide on the fill-in.

Lovett "hopes that portion of Judge Leone's order is reversed. And she hopes once the Republicans assemble, she may be that person they select," he said.

Contact staff writer James Osborne at 856-779-3876 or jaosborne@phillynews.com.

Inquirer staff writer Matt Katz contributed to this article.