Peter Wright, the outgoing president of the Scottish Secondary Teachers' Association (SSTA), will describe the new curriculum as "not capable of delivering" for parents, pupils or teachers.
The Curriculum for Excellence was introduced in all schools in Scotland last August after a year's delay to give teachers more time to prepare for it.
The new system has been plagued by criticism that it is "vague" and "woolly" since the idea was first mooted nearly a decade ago. In his final speech as president of the union, Mr Wright will also criticise the new qualifications which are being introduced to fit into the new system.
He will warn the re-elected SNP government that Curriculum for Excellence is "unfinished business" for the SSTA.
"We will not let go until our members tell us to do so."
Mr Wright will also be critical of cuts to education across Scotland.
He will single out Prime Minister David Cameron's coalition government at Westminster for attacking teachers' pensions.
He said the average teacher's pension was just 9,000 and dismissed the myth that they were "gold plated".
He criticised the Prime Minister for previously vowing not to touch the pension rights already accrued by teachers.
He said: "Mr Cameron, you have taken thousands from my pension and from the pensions of every other teacher in Scotland. You have attacked our accrued rights.
"In my book, that makes you a hypocrite or worse: a liar and a thief."
Key issues expected to be discussed at the union's annual congress in Peebles include the curriculum, new exams and proposed changes to teachers' pay and working conditions.
He will say: "Why is it that the SNP Scottish government and both Labour and SNP councils have conspired to attack the living standards of Scotland's teachers and bring about a destruction of their conditions of service which will last well beyond the present economic crisis?"
"The SSTA rejected these proposals and the others because they were simply unacceptable to our members."
A Scottish Government spokesman said: "Curriculum for Excellence is energising learning and teaching in Scotland, giving young people the skills, knowledge and understanding they need to succeed in learning, life and work.
"It has been introduced to raise standards and help improve our children and young people's life chances through making learning and teaching more relevant, exciting and engaging."It is here to stay and encourages teachers and other practitioners to use their professional expertise and creativity to show how curriculum subjects and areas can be linked, just as they are in life and work."?
A Treasury spokesman said: "We are protecting accrued pension rights and it is wrong to suggest otherwise."