Women will have to pay for pap smears under changes to rebates for pathology services, Labor and the Greens have warned.

The federal government announced in its budget update in December that it would scrap the bulk-billing incentive it pays to health professionals for pathology services and reduce the incentive for diagnostic imaging.

The changes will apply to pap smears, because although the procedure is commonly preformed by GPs, the samples taken by doctors are sent to pathology companies to be analysed.

The opposition health spokeswoman, Catherine King, warned that scrapping the incentive payment would have a “direct impact on women’s health”.

“Pap smears continue to be a very important health measure that stops cervical cancer, and we want to encourage women to have their regular pap smears,” King said on Wednesday. “[Reducing bulk-billing incentives] will of course put a barrier to women accessing this very important preventative measure.”

Only 50% of women in the eligible age group for pap smears undergo the procedure and additional costs would prevent even more electing to have the test, King said.

An online petition calling on the government to halt the changes to the incentive payments was created on Tuesday afternoon. Less than 24 hours later, it had 29,000 signatures.

The petition cites the president of the Royal College of Pathologists Australasia, Michael Harrison, as saying pap smears could cost women $30, and magnetic resonance imaging (MRI) could cost $173.

“These cuts are unfair to the average Australian, but will especially hurt women,” said the author of the petition and official of the New South Wales branch of the National Teritiary Education Union, Brigitte Garozzo.

“Free and accessible pathology tests are key to ensuring early detection of cervical cancer, sexually transmitted infections, urinary tract infections and pregnancy.”

The Greens leader, Richard Di Natale, a former GP, said reducing the payments would mean women seeking pap smears would have to pay extra.

“To put an upfront charge in front of important medical technologies and interventions ... is putting a barrier in front of women,” he said.

“It is critical that the government realises that its cuts to pathology, and indeed the cuts to the healthcare sector, are having a damaging impact.”

The health minister, Sussan Ley, rejected suggestions that the government was reducing the Medicare rebate that patients get for doctors’ visits.

RT fyi NO cut 2 $ value of Medicare Rebate YOU receive 4 pap smear/test or your access to it as falsely claimed 2day #papsmears #auspol — Sussan Ley (@sussanley) January 6, 2016

“There are no changes proposed in Myefo regarding the cost of either receiving or delivering a physical pap smear examination undertaken by your GP or specialist, nor their billing practices,” Ley said in a statement.

“Changes in Myefo relate to an inefficient payment – worth between $1.40 and $3.40 – that is paid direct to pathology corporations separate to the Medicare rebate.”

The incentive was introduced by the then Labor government in 2009 as a way of maintaining and increasing bulk-billing rates for pathology and diagnostic services.

Last month Ley admitted some patients could be worse off with the changes, but said it was up to competitive pathology companies to absorb the shortfall.

MYEFO changes about inefficient payment 2 pathology corporations, complaining bout impact on shareholders. Medicare not corporate bankroll — Sussan Ley (@sussanley) January 6, 2016

“Medicare is not designed to be a guaranteed bankable revenue for corporations, nor is a taxpayer-funded payment like this provided to cross-subsidise other costs of doing business for pathology companies,” she said on Wednesday.

Pathology companies say they will have no choice but to charge patients a co-payment for services such as blood tests, saying there is “no fat in the system” to absorb the costs.

Ley rubbished that.

“Alleged claims by pathologists about the potential cost of raising their prices as a result of any changes are also misleading, because they have omitted the value of the Medicare rebate a patient receives from the government to help cover this very cost,” she said.

“It is important to acknowledge complaints from stock exchange-listed pathology companies about this Myefo decision have revolved around impacts on ‘shareholders’ – not patients – exposing what is really motivating these criticisms.”

Labor has vowed to oppose the changes, despite the fact they will be introduced by regulation and therefore do not require legislative oversight.

“Everything this government does means that costs are transferred on to patients and that is what we’re told is going to happen with these measures,” King said.

“The end result is that patients will pay.

“We are calling on the government to give the Senate a clear opportunity to debate [the changes].”

The changes come into effect on 1 July.