Katie Ascough is facing the vote after removing abortion information from a student handbook
The UCD Students' Union president has told students she is "willing, ready, and determined" to return to her job if they vote against her impeachment.
Since yesterday, students at the Dublin university have been voting in a referendum over Katie Ascough's presidency.
Photos from the campus today showed long queues of students waiting to cast their votes.
Ms Ascough - who only took over the role several months ago - became embroiled in controversy over her decision to remove information about abortion from a student handbook.
She insists that her executive decision to edit the information and reprint thousands of handbooks - at a reported cost of up to €8,000 - was made after she received legal advice that the information was illegal.
Ms Ascough - who is a prominent pro-life campaigner - pledged during her campaign that she would respect the union's pro-choice mandate over her own personal views on abortion.
On the subject of the reprint, she has argued: "I was not comfortable putting myself and others at risk - risks that were real, that were written in legal advice, and that I, very genuinely, was worried about."
Campaigners for her impeachment have argued that that it was unlikely that the information would have resulted in any legal penalties, pointing out similar information was printed last year without any consequences.
Four of Ms Ascough's fellow SU sabbatical officers are among those campaigning for her impeachment - although they temporarily ceased canvassing in recent days after being denied permission for annual leave.
They are due to return to campaigning before polls close tonight:
We have received confirmation that the Returning Officer has given permission for the sabbatical officers (Barry Murphy, Niall Torris, Rob Sweeney and Eoghan MacDomhaill) to campaign for impeachment after 5pm today. #ImpeachmentReferendum— College Tribune (@CollegeTribune) October 26, 2017
In a lengthy open letter to students today, Ms Ascough wrote: "I ran on a platform of things like cutting the cost of college and improving mental health supports. I did not agree to break the law and run the risk of a criminal record for the rest of my life.
"I have put my whole heart and soul into being your SU President for the last four months. UCD is an incredible place, and I am so grateful to be elected to represent the 30,000+ amazing students of UCD. You have my commitment, you have my all."
Meanwhile, Roisin Guyett-Nicholson, a former editor of the University Observer, argues in an opinion piece for the campus newspaper: "The union right now is not representing students and even worse than that, they are undermining their ability to address problems going forward or strengthen their position in future.
"For their education alone, students deserve a better President and a better union than they currently have."
Voting is open on campus until 8pm, with early results expected later tonight.