Five candidates are contesting the West Tyrone by-election.
Nominations closed on Tuesday for the by-election, which will be held on May 3.
It was called after the resignation of Sinn Fein's Barry McElduff over his Kingsmill loaf tweet
They include Sinn Fein's Orfhlaith Begley, who is defending a 10,000-plus majority in a seat where the party took just over 50% of votes cast in last year's general election.
Thomas Buchanan is contesting the seat for the DUP, Stephen Donnelly for the Alliance, Daniel McCrossan for the SDLP and Chris Smyth for the UUP.
Former MP Mr McElduff quit in January, 10 days after a controversy flared when he posted a video of himself with a Kingsmill-branded loaf on his head on the anniversary of the 1976 Kingsmill massacre.
He insisted it was not an intentional reference to the murders of 10 Protestant workmen by republican paramilitaries, but he acknowledged he had caused hurt and offence to victims' families.
Sinn Fein vice president Michelle O'Neill has said she expects a strong showing, portraying the poll as the first chance for voters to cast judgment on the breakdown of the Stormont talks process.
When she accompanied Carrickmore solicitor Ms Begley as she lodged her nomination papers in Omagh last Thursday, she said she did not expect the tweet controversy to affect Sinn Fein's vote.
She said: "Barry did the right thing when he realised there was an error of judgment.
"He did the wrong thing, it wasn't intentional, but he himself recognised that hurt was caused, he took action, he stood out of political office, which is a big decision for anybody to take.
"We wish Barry well in the future but this is now an election in West Tyrone about Orfhlaith Begley, this is about getting Orfhlaith Begley elected."