Charities that support children leaving care have called on ministers to end the postcode lottery surrounding whether they pay council tax.
Seven of Wales' 22 councils are exempting care leavers from paying the tax from the start of April - some until the age of 21 and others to 25.
But charities including The Children's Society and Voices From Care Cymru said it should be brought in everywhere.
The Welsh Government said the decision remained with each local authority.
The charities have called on Welsh ministers to follow the Scottish government's lead, saying it would end confusion and ensure all care leavers were treated equally, no matter where they lived.
The Children's Society, which has been discussing the issue with AMs, said it would give a helping hand to some of the most vulnerable members of society.
"We know that many care leavers live on their own from the age of 18, which is completely different to many other young people," said local campaigns manager Sarah Wayman.
"Having debts hanging over your head can result in bailiffs and court action, which can become increasingly stressful for a young person who doesn't have any support."
She added about 70 councils in England had brought in exemptions.
So far in Wales seven of the councils who responded to BBC Wales' request for information have said they will not charge care leavers for council tax:
- Anglesey said they would be exempt until they reach 21, as they will be in Torfaen, although there will be a discretionary option to extend this to 25
- Bridgend, Cardiff, Caerphilly, Carmarthenshire and Rhondda Cynon Taf have exempted care leavers until 25
Other councils, including Vale of Glamorgan and Ceredigion, said their cabinets would be considering the issue in the near future, while others said they were not introducing an exemption.
Christopher Dunn, programmes manager at Voices From Care Cymru, said: "The exemption should be across the board, without a doubt.
"We're looking to write to all the council leaders to say 'what are you doing about it?'
"How will it work in practise without an exemption across Wales? If a care leaver from Cardiff then moves to Bridgend will they still be exempt?
"It's very confusing and I'm sure we will get young people contacting us for help with this when it kicks in properly."
Barnardo's Cymru said it recently delivered a report to ministers calling on support for care leavers to continue until they are 25.
Sarah Crawley, its director, said vulnerable people leaving care can struggle to gain employment, training opportunities and good quality accommodation.
"They should not have the extra burden of council tax which could exacerbate their financial challenges and affect their ability to live healthy, independent lives," she added.
The measure is also supported by the Children's Commissioner for Wales, Sally Holland, as expressed in her Hidden Ambitions report.
There are about 16,000 children in care in Wales, according to last year's Wales Children Receiving Care and Support Census and local authorities have a duty to of care to them as their corporate parents.
The Welsh Government said it was committed to supporting care leavers.
"Regulations are in place which enable local authorities to exempt care leavers from paying council tax. The decision on whether to adopt the exemption is a matter for each local authority," a spokesman said.
"We are pleased a number of local authorities in Wales have already agreed to exempt care leavers from council tax.
"We are continuing to liaise with the WLGA on this issue and will be seeking clarity from them on what the remaining local authorities are intending to do."