At the moment, students and examiners have to wear a gown over an outfit known as "sub fusc".
The compulsory clothing includes a dark suit, black shoes, a plain white shirt or blouse with a bow tie, long tie or ribbon.
Oxford University Student Union has called a referendum on the rules.
The result of the online vote will be announced on Friday at 20:00 BST.
James Blythe, the union's vice-president for access and academic affairs, said he called the vote after some examiners asked to be allowed to stop wearing sub fusc.
He said the policy should only be changed if it also applied to students.
At a previous referendum in 2006, students voted to continue the tradition.
A "no" vote would not automatically change the rules, as the result is not binding on the university.
Xav Cohen, a second-year student of Philosophy, Politics and Economics, who is leading the "no" campaign, said: "I think people see sub fusc and they associate it with the perceived elitism at Oxford of the Bullingdon Club and all the rest of it.
"They see it as inaccessible and quite alienating and a lot of really able students, when they're 16 or 17, think, because of the traditions, 'this place isn't for me'."
First-year History student Harrison Edmonds, leader of the "Save Subfusc" campaign, said: "The thing about sub fusc is that it doesn't matter about your background, your gender, your class, your race - it treats you all equally.
"It is an Oxford tradition that is popular with students and... it is one of our unique selling points as a university."
The University of Oxford has declined to comment ahead of polls closing.
Sub fusc comes from the Latin for dark brown.
The first reference to the term is in the university statutes from 1636.
The University of Oxford defines it as:
1.    one of: dark suit with dark socks; or dark skirt with black tights or stockings; or dark trousers with dark socks
2.    dark coat if required
3.    black shoes
4.    plain white collared shirt or blouse
5.    white bow tie, black bow tie, black full-length tie, or black ribbon.
Source: http://www.ox.ac.uk/students/academic_dress
Students at Oxford University are voting on whether or not they should continue being forced to wear special clothes to sit their exams.