The charity's second State of the Nation's Foster Care report, based on a survey of more than 2,500 UK foster carers, found that the proportion of foster carers who would definitely recommend fostering to others had fallen from 66 per cent in 2014 to 55 per cent in 2016.
Meanwhile, a third of foster carers felt that children's social workers did not treat them as an equal member of the team.
And only 42 per cent of foster carers felt their allowance covered the full cost of looking after fostered children - compared with 80 per cent in 2014
One in three foster carers described out of hours support as either "could be better" or "poor", and 31 per cent of foster carers reported that they were rarely or never given all the information about a fostered child prior to their arrival.
In addition, around one in six foster carers (17 per cent) under the age of 55 said they were likely to quit the role within five years.
Kevin Williams, chief executive of The Fostering Network, who is due to appear before the education select committee tomorrow as it holds a public evidence session as part of its inquiry into fostering, said government is responsible for providing adequate funding to local authorities to enable them to support foster carers.
"The government agenda on austerity has led people to make decisions that impact on fostering recruitment," he said.
"Our findings tell us there is a strain on fostering services. There will be continued problems in recruitment and retention. This is not in children's best interests, and the state faces a higher cost financially."
He also warned that the proportion of foster carers set to retire would be larger as the survey did not count those aged over 55.
"This is a significant percentage that will stop over the next five years," he warned.
Charlotte Ramsden chair of the health, care and additional needs policy committee at the Association of Directors of Children's Services, said cuts to foster caring are being "exacerbated by some independent fostering agencies in the private for-profit fostering sector taking a disproportionate amount of money out of the foster care system.
She said this could otherwise be re-invested into improving foster care and outcomes for vulnerable children and young people.
Andy Elvin, chief executive of The Adolescent and Children's Trust (Tact) said foster carers should be respected as "experts on their child by social workers, teachers, health professionals and the family courts."
"There is no excuse for poor communication with those caring for the child," he said.
"We too are very concerned that some local authorities are seeking to cut fostering allowances and this must stop."
However, he questioned the research's findings about how many foster carers would recommend fostering, pointing to a Tact survey of about 380 carers of which 96 per cent said they would recommend fostering.
A Department for Education spokesperson said: "Foster carers make an essential contribution to children's lives and we want to ensure they receive the support they need.
"That is why we are currently undertaking a national stocktake of fostering to better understand current provision - including looking at issues affecting foster carers, such as fees, allowances and support.
"Alongside this we have supported the testing of new and innovative models of foster care as part of the £200m children's social care innovation programme, including better ways to support children in foster care and their carers."