The federal government wants single parents moved to the Newstart allowance when their youngest child turns eight. The changes would save the government $728 million over four years.
The government says the policy will encourage parents with school-age children to re-enter the workforce sooner.
The Parliamentary Joint Committee on Human Rights has said the government should defer these measures until the outcome of an inquiry into the adequacy of Newstart is known.
"The committee is not yet convinced by the government's assertion that all affected individuals will maintain access to appropriate levels of social security support," the committee said in its report tabled in the Senate.
Australian Greens senator Rachel Siewert said mothers moving from the single-parent payment to Newstart could end up significantly worse off as they would be paid less and, if working, could earn less.
"Far from encouraging people into work, it can discourage people from seeking work because they gain less benefit from being in part-time work," she said.
Senator Siewert said 45 per cent of single parents receiving parenting payments were actually working.
In August, the Senate's education, employment and workplace relations legislation committee also recommended the changes be put on the backburner.
Comment has been sought from Workplace Relations Minister Bill Shorten's office.