Iran's supreme leader has called for a population increase in an edict likely to restrict access to contraception that critics fear could damage women's rights and public health.

In his 14-point decree, Ayatollah Ali Khamenei said increasing Iran's 76 million-strong population would strengthen national identity and counter undesirable aspects of western lifestyles. "Given the importance of population size in sovereign might and economic progress … firm, quick and efficient steps must be taken to offset the steep fall in birth rate of recent years," he wrote on his website.

Khamenei's order, which must be applied by all three branches of government, replaces the "fewer kids, better life" motto adopted in the late 1980s when contraception was made widely available.

Since then the birth rate has fallen from 3.2% in 1986 to 1.2%, according to the CIA World Factbook. At current fertility rates, Iran's median age is expected to increase from 28 in 2013 to 40 by 2030, according to UN data.

But many Iranians are concerned about policy shifts to boost the population, something proposed for years by conservatives, including the former president Mahmoud Ahmadinejad, who favoured nearly doubling the population to 120 million, encouraging women to stay home and devote their time to child-rearing.

Reformist Iranians fear the fertility campaign could undermine the position of women in a country where 60% of university students are female but only 12.4% of the workforce is, according to the Statistical Centre of Iran.

There are also fears about sexual health. "In order to fight Aids, our only route is to distribute and teach people to use condoms," Dr Minoo Moharez, head of the Aids research centre at Tehran University told Shargh daily. "If, based on some policies, the distribution of condoms in the country is faced with limitations, it will cause horrible events, the increase of Aids patients from unprotected sex will be compounded."

Fertility is one of many issues that divides conservatives and reformists in Iran, where President Hassan Rouhani has called for as easing of social restrictions. He has said little on birth control, focusing his attention on negotiating a deal with world powers on Iran's nuclear programme in order to escape economic sanctions.

Farzaneh Roudi of the Population Reference Bureau, a Washington-based thinktank, said if Tehran was concerned about an aging workforce, it would employ more women. "The government could tap the women labour force, many of whom do not work in the formal economy," she said.

Roudi added that the political push for a baby boom was unlikely to succeed. "It's hard for me to imagine that people will have more children because Khamenei wants them to."