The National Education Union (NEU) surveyed more than 900 teachers and other school staff in March, finding that half are reporting that their schools are making cutbacks to the SEND support for pupils, compared with 40 per cent reporting cuts in 2017.
The biggest rise is in primary schools where 54 per cent are reporting cuts, up markedly on 37 per cent in 2017.
Among secondary school-based respondents 49 per cent said they are experiencing SEND cuts, compared with 44 per cent the previous year.
The union's survey also found that a third (31 per cent) of schools are cutting SEND posts this year, compared with a quarter (26 per cent) last year. Among secondary school staff 36 per cent are reporting cuts to SEND staff this year.
In addition, primary schools are struggling to access external SEND support, with 39 per cent reporting problems in bringing in outside expertise, compared with 15 per cent in secondary schools saying this was a challenge.
"If the true measure of a country is how it treats its most vulnerable, then this government is failing big time. Children with special needs are being let down," said NEU joint general secretary Dr Mary Bousted.
"The government's funding cuts are cutting so deep that schools cannot provide the support SEND pupils need and are struggling to access external support because this has been cut too.
"The government needs to wake up to the facts and urgently make more money available for schools so they can keep SEND pupils safe and provide the help and support they need."
Last month former children's minister Edward Timpson was appointed to lead a government review into school exclusions.
This followed concerns raised by Ofsted about local variations in school exclusion rates. The inspectorate wrote to more than 100 head teachers in eight exclusion "hot spots" criticising the high number of pupils being removed from schools in their area.
Another concern of government is the use of informal exclusions through "off rolling", whereby schools encourage parents of challenging pupils to take up home schooling.
This is among issues being looked at in a government consultation on home education, which was announced this week.