The comments highlight the financial pressures on families and on the Iranian government, despite this month's nuclear deal with world powers that could pave the way for an economic rebound.
An austerity budget passed in March after a precipitous drop in global oil prices has left key Tehran ministries, including education and oil, struggling to pay wages.
A new law enshrining nine months of paid leave for mothers has been passed yet there are no funds to pay its estimated 3.2 trillion rial ($985 million) bill, according to welfare bosses.
"So far, not one rial has been allocated," Mohammad Hassan Zeda, a deputy at Iran's Social Security Organisation, told the ISNA news agency in an interview.
He said studies showed that from 145,000 women who had gone on a six-month maternity leave in the past 18 months, 47,000 of them -- almost a third -- were sacked when they tried to return.
"This is because right now due to the situation in the job market, there are many individuals with higher education who are prepared to work for lower salaries," said Zeda, noting the trend would likely worsen.
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"If maternity leave is increased to nine months, the number of women getting sacked, upon returning to work after using maternity leave, will increase much more."
According to the Statistical Centre of Iran, the unemployment rate was 10.8 percent in 2014, though unofficial sources estimate the number is as high as 20 percent.
Unemployment is particularly bad among women (19.2 percent) and youths (25 percent).
Underemployment has also become common in Iran, according to the World Bank, with a weak labour market leaving only 36.7 percent of the population economically active.
Zeda said the nine-month maternity leave term can start if the government allocates the money, but officials are "not allowed to implement a law for which no financial resources have been provided."
Around 160,000 working women would be eligible for the nine-month leave, he said.
After a deep recession, Iran returned to growth of three percent last year, partly due to limited sanctions relief under an interim nuclear deal between Iran and six world powers.
A final deal struck on July 14 in Vienna stands to lift all UN, US and Europeans sanctions imposed on Iran as punishment for its disputed nuclear activities, raising hopes of better economic and job prospects.