The university council signed off on the proposal at a meeting yesterday amid concerns about the university’s financial stability.
Mr Robertson said he brought the proposal to the table "with a heavy heart".
"This is not a paper that brings me any joy.
"As a university, we do care deeply about the fact the cost-of-living pressures are acute for many of our students."
Mr Robertson said the university was attempting, in its own way, to address some of the hardship issues through special scholarships, but the university also had to take steps to reduce its own deficits.
"It appears that all universities are taking up this [6%] increase.
He also warned of possible further job cuts if the university did not increase fees.
The motion was passed almost unanimously - Otago University Students’ Association president Keegan Wells abstained.
Ms Wells said she acknowledged the work of the university council and the financial position of the university.
"But let’s not make this increase a habit. This kind of sucks," Ms Wells said.
Council member Clare Curran said she accepted the recommendation, but wanted to "register discomfort at the exercise" and the level of costs passed on to students.
When the Otago Daily Times spoke to students on campus, none of them agreed with the decision.
Hannah Armstrong, a third-year student, said the situation "sucked", especially after all the money she had provided to the university.
Ponui McConachy said he acknowledged the university sometimes needed to operate like a business, but felt it should consider the cost-of-living issues of students.
Postgraduate student Mena Talalima wondered whether she might have to seek out other means of funding to keep up with cost pressures.
Student Siunari’i Paiva said she felt sorry for her parents, who helped pay for her fees.
"The setting of tuition fees for 2025 comes during a challenging time for the university, as it seeks to recover from the financial deficits of recent years and to return to a financial surplus that will enable future investment in strategic priorities.
"Equally, it is important to acknowledge that this a challenging time for students, who face a significant change to the government’s fees-free policies, as well as general cost increases."
Student-related income for domestic students is primarily based on two components — the funding provided directly to universities by the government and the tuition fee component charged to students.
The paper noted the 6% increase was well above the present rate of inflation, which is estimated to be about 3%, but said this ignored the fact that since 2018 university tuition fees had not kept up with inflation — and in order to "catch up", fees would need to increase 20% this year.
"Viewed in this context, the increase offers the option of a partial catch-up for previous years in which permitted fee increases were well below CPI [consumers price index]."
The university has faced significant financial challenges in the past two years; and has laid off hundreds of staff after lower-than-budgeted student numbers led to decreased revenue.
"Government has approved a 6% increase in part to provide universities with a means of easing their current financial pressures. Should Otago fail to take full advantage of this, it would send an awkward message to government and the Tertiary Education Commission in respect of our fiscal prudence," the discussion paper said.
"Our present understanding is that most if not all other New Zealand universities will increase fees by the maximum 6% permitted for 2025."
The discussion paper also acknowledged the likely increased financial burden on students, but said some of this would be mitigated by a $45million investment in scholarships over the next year.
The yearly increase in undergraduate fees for students ranges from $393 (for an arts student) to $1043 (for a dentistry or medical student).
Meanwhile, the university is also considering whether or not to increase its activity fees by 7% to $1152.
"Despite our efforts to minimise expenses without compromising service quality, the costs of providing these services to students continue to rise. This increase has received support from the student body," the paper said.
