BELGRADE (AFP) - A Serbian doctor has thrown a spotlight on a "discriminatory" new law with a dramatic pledge to change sex after she was told to retire earlier than her male colleagues.

Mirjana Stanojcic, 64, was informed by her hospital bosses in central Serbia that she would have to hang up her white coat this month when the legislation came into force.

The law passed in July - in a bid to trim the Balkan country's bloated state budget - requires female public sector employees to retire at 60 years and six months, while men can work until they are 65.

Previously both sexes could continue working beyond the retirement age if they wished to do so.

"I have a male colleague who is the same age as I am, and I have been told to retire while he will keep working," said Stanojcic.

"I decided to become a man and keep working in accordance with the law."

Stanojcic, a physical therapy specialist in the small town of Gornji Milanovac, has received widespread media attention in Serbia since applying for the lengthy process of sex reassignment.

Following the press coverage, along with appeals from Serbia's ombudsman and the equalities commissioner, the constitutional court has suspended the new law's enforcement until it makes a final ruling.

Stanojcic was buoyed by the suspension but said she would continue with the sex change procedure - even though she would be over 65 on its completion.

"I do not know what the final court decision will be, so I will keep going," she said, adding that her move had won support from female colleagues across the country.

Reports of the doctor's plans have been met with concern from transgender rights activists in Belgrade.

A statement from the group Gayten-LGBT said that using gender discrimination at work as the only reason for a sex change "trivialises the lives of transgender people who are one of the most marginalised groups in Serbia".

Despite this stigma in the conservative nation, Serbia's capital has grown in recent years as a centre for sex change surgery, which is often cheaper and more easily available than in other countries.

Operations for Serbian patients are subsidised by the state, and come at the end of a two-year procedure that includes a psychological evaluation.

Surgeon Dusan Stanojevic, a sex change specialist who went to school with Stanojcic, told the Beta news agency he would operate "pro bono" for his friend as "this was the first time someone applied for such a procedure for an economic reason".

Currently around 10 percent of Serbia's 7.2 million people are state employees.

As a part of a three-year 1.2 billion euro (S$1.91 billion) loan arrangement with the International Monetary Fund, the country has to reform its public sector and cut employee numbers by 15 per cent by 2017.

A separate law passed last year for all Serbian workers is gradually raising women's retirement age from 60.5 to 65, the same as men's, by the year 2032 - but such equality will come too late for Stanojcic.

"Woman are being discriminated against on various grounds and that should be stopped once and for all," she said.