HARRISBURG, Pa. (AP) — More than 2,000 undated mail-in ballots cannot be counted in a western Pennsylvania state Senate race, an appeals court ruled Thursday, saying handwritten dates “provide a measure of security.”

The 2-1 Commonwealth Court decision could swing the neck-and-neck contest in which Republican challenger Nicole Ziccarelli trails narrowly against Sen. Jim Brewster, D-Allegheny.

Judge Kevin Brobson, a Republican, said to ignore the requirement that mail-in voters date the outside of return envelopes “would constitute a judicial rewrite of the statute.”

In a dissent, the panel's lone Democrat, Judge Michael Wojcik said a blank or even simply unsigned declaration on the outer envelope would be disqualifying, but the ballots are time-stamped.

“I view the requirement of a voter-inserted date on the declaration as similar to the issue of the color of ink that is used to fill in the ballot,” Wojcik wrote.

The case was sent back to Allegheny County.

The issue, however, is already at the Pennsylvania Supreme Court, which on Wednesday agreed to hear a case involving Republican President Donald Trump's campaign seeking to have more than 8,000 ballots disqualified in Philadelphia because voters who signed their ballots failed to also handwrite their names, addresses or the date.

Ziccarelli is currently down by just 17 votes against Brewster, a former banker first elected to the Senate 10 years ago, in a race The Associated Press has not yet called.

With more than 131,000 votes cast in Allegheny and Westmoreland counties, a district that runs down the Alle-Kiski Valley, Brewster's lead is a razor-thin 50.01% to 49.99%.

Ziccarelli also has a lawsuit pending in Westmoreland County that argues elections officials in that part of the Senate district treated mail-in ballots without secrecy envelopes inconsistently and improperly counted some provisional ballots.

In that case, she argues the elections board should not have allowed all votes to count from voters who had to cast provisional ballots and were also directed to sign the poll book. The signatures on a precinct's poll book make it unclear whether those voters also cast a conventional voting machine vote.

Brewster, a former mayor of McKeesport, is the ranking Democrat on the Law and Justice and Game and Fisheries committees. Ziccarelli is a lawyer from New Kensington.

The state Senate is days from the end of its current term, with Republicans holding a 28-21 majority, along with an independent who caucuses with the GOP. A Ziccarelli win would give Republicans a 30-20 working majority in January.