Personal statements from respondents suggest the students also believe their loan debt will affect more than one aspect of family life.
Some said the debt meant delaying home ownership, which was seen as essential for starting a family.
One student said: "I won't have children because I wouldn't be able to provide for them as long as I've got this debt."
Another spoke of a different impact: "If you waited until you were financially stable you would be too old to have children. That's the reality of study today."
Others said it would not affect their decision to have children, but would make raising them harder.
Union president Rory McCourt said "user-pays education" was causing unintended consequences on New Zealand society.
"What this research shows is that toxic student debt is removing choices for New Zealand families. They're delaying, deferring and deserting starting a family because of mounting debt."
Mr McCourt said the 12 cent loan repayment rate was excessive.
The rate, which applies to every dollar earned above $19,084 annually, or $367 a week, was punishing for graduates and forcing them to make decisions like delaying starting a family, he said.
"Our repayment threshold was originally set to ensure the poorest New Zealanders didn't have impossible repayment obligations. By not adjusting it we've increased the effective marginal tax rate for minimum wage workers to above that of the vice-chancellor and the Prime Minister. That is deeply wrong."
He said a progressive repayment scheme was needed. "In Australia, graduates don't pay a cent until they earn $54,126, and even then it's only 4 per cent of their income. From there it goes up 0.5 per cent for every additional $6000 earned."
Tertiary Education Minister Steven Joyce dismissed the survey as unscientific.
"Scientific research from the Universities of Canterbury and Otago show there is no statistical evidence that having a student loan has any actual impact on child-bearing trends."
Baby stretches precious funds
Massey University student Ella Cartwright, 24, had an unplanned pregnancy during her studies.
She is continuing her degree but has detailed the financial difficulties students face when they have children early.
"My partner and I had an unexpected pregnancy before either of us had completed our education. We want to ... build a solid future for our child, but finances are really difficult.
"We are limited as to how much childcare we can afford to put our daughter in, so I have to study from home while she is there with me, making it really hard to keep up."
Ms Cartwright said the student allowance was split between the couple, so they both worked to top up their income.
"Which means we are busy and stressed all the time. I'm in my second year now ... and my grades are falling.
"And we are the lucky ones - we rent off a family member for a reduced rate, and my partner's parents give us a little money every week."
Ms Cartwright said without those things, pursuing higher education would be impossible.
"We have to forfeit expenses like medical care or prescriptions, replacing clothing, or keeping fresh food in the house. Neither of us can afford to socialise."
