The number of families in Wales helped by a grant scheme for those with ill or disabled children has fallen by two thirds after cuts in funding.
Family Fund was promised £1.5m over three years by the Welsh Government in 2016, down from £2.5m a year.
The number of families helped fell from 5,429 in 2015/16 to 1,686 in 2016/17, which Plaid Cymru called "the heartbreaking effect of Labour's cuts".
The Welsh Government said Family Fund was given the maximum available.
Parents or carers on a range of benefits or with low incomes can apply for grants to pay for furniture and electrical appliances, days out and holidays, and specialist toys or computers.
Since April 2016, Family Fund has said that due to the reduction in money available in Wales, it will prioritise families who have not previously been helped by the scheme.
Applications from other parts of the UK have not been affected by funding cuts.
Plaid Cymru accused Labour ministers of denying any problem when they voted against a motion to reverse the cuts in a Senedd debate in March.
Health spokesman Rhun ap Iorwerth said: "Because of Labour's decision to cut the fund, 3,700 fewer of these families have been helped this year compared to last. This is the heartbreaking effect of Labour's cuts.
"What makes it worse is Labour's refusal to accept that there has been a cut in support.
"The entire sector had warned that changes to the way the Family Fund was to be financed would mean thousands of the poorest families with disabled children would lose out.
"Yet Labour ignored these warnings and not only went ahead with the cuts, but refused to acknowledge making the mistake when Plaid Cymru tried to make them see sense.
"Now we know for sure the extent to which the changes have harmed these families, I cannot see why the cuts can't be reversed."
A Welsh Government spokesperson said: "This is not a new story. Plaid Cymru held a debate in the Assembly in March of this year and nothing has changed since then.
"At that time we made it clear that the Sustainable Social Services Third Sector Grant Scheme has brought together funding from four previous grant schemes to help third sector organisations deliver our ambitious agenda for social services in Wales.
"Given that there was a great deal of interest in the scheme, with applications significantly outstripping the funding available, a decision was taken to limit the maximum grant available to any single project to £1.5m over three years.
"As part of a competitive application process, Family Fund was awarded the maximum amount of funding available. While we appreciate that the grant awarded is less than the grant the Family Fund previously received in Wales, we have also provided an additional £400,000 to enable the organisation to refocus its grant model and to seek alternative funding sources."
The spokesperson added that, overall, nearly £22m had been awarded for the three years (2016-2019) to more than 30 social services projects under the new scheme.
Family Fund said funding remained at the same level year-on-year for England, Scotland and Northern Ireland with little change in the numbers of families helped in those nations.
Chief executive Cheryl Ward said: "We appreciate that very difficult decisions have had to be made with reduced budgets in Wales.
"We remain committed to doing all we can and making the very most of every penny of funding available, and are seeking further funding to support the families that need us."