Public Health Wales has apologised and admitted it hasn't "done enough" to explain the reasons for increasing the length of time between cervical screening tests.
The change, which was announced on Tuesday, means people aged between 25 and 50 with a cervix will now wait five years until another test, rather than three, providing no human papillomavirus (HPV) cells are detected.
Certain types of 'high-risk' HPV cells can cause changes to the cells of a cervix, but early detection means the individual can receive treatment before the cells turn into cancer.
Health officials said the length of time between tests is being extended because of the success of more effective HPV testing.
But the announcement has been met anger and concern, sparking a petition that has gained more than 150,000 signatures in just over 24 hours.
In a social media post, Public Health Wales said: "We are sorry. We haven't done enough to explain the changes to cervical screening and have caused concern.
"We are working to make this clearer and more information will be available as soon as we can today and in the coming days."
There are around 850 cervical cancer deaths in the UK every year, according to Cancer Research UK.
99.8% of cervical cancer cases in the UK are preventable.
In the announcement, Heather Lewis, Consultant in Public Health for Cervical Screening Wales explained: "The HPV test we now use in Wales is more effective at identifying people at higher risk of developing cell changes which can cause cervical cancer.
"The evidence shows that it is therefore safe to extend the time between cervical screening tests for people who do not have HPV identified."
HPV testing was introduced in Wales in 2018 and almost nine out of ten results show no high-risk HPV.
HPV is a common virus that most people will come into contact with at some point during their lives. One or more high-risk types of HPV are present in over 99.8% of cervical cancers.
Louise Dunk, Head of Programme for Cervical Screening Wales at Public Health Wales said: "It is a really positive development that this more effective test will mean that women and people with a cervix, who test negative for HPV, now only need to attend their testing every five years, rather than three."
But the extension has been accused of "putting lives at risk", with many opponents from around the UK sharing their experience of cervical smearing and cancer on the petition page.
Patricia Preece, from Treherbert, wrote: "I'm signing because my 42-year-old sister-in-law died from cervical cancer.
"It is very important to have smears and be able to catch the early onset of cancer so more women can survive."
Cath Rees, from Brecon, added: "I've had treatment for abnormal cells that were detected early by a routine smear test.
"So important to have regular smear tests. Surely cheaper to prevent then try to cure."
Lianne Snelson, from Sandbach, said: "As someone who has had abnormal cells in the past, the idea of five yearly screening is simply terrifying and dangerous!"
The decision has also attracted criticism from the Welsh Conservatives.
Shadow Health Minister Russell George said: "While I am pleased to see HPV checks become more reliable and effective, I find it difficult to see why this change is necessary.
"Hopefully, the Labour Government is not using this as a chance for penny pinching, because more effective tests will only be more effective if conducted more regularly.
"Once every three years is hardly a burden on women who want peace-of-mind and should not be one for NHS.
"The way this petition has taken off and the strength of feeling out there should surely force the Labour Government to at least re-consider the changes they propose to make regarding these life-saving checks."