Scrapping the Education Maintenance Allowance (EMA) could lead to a "colossal waste of talent".
Dr Mary Bousted, general secretary of the Association of Teachers and Lecturers, said the government is taking an unnecessary gamble with people's lives by cutting a payment that helps disadvantaged pupils cover their college expenses.
She claimed that without this money, many youngsters will be forced to leave education when they reach the age of 16.
"This would be a colossal waste of talent, condemn many young people to unemployment, and would be a completely false economy resulting in higher unemployment among young people, college closures and redundancies among lecturers," Dr Bousted added.
Speaking earlier this week, University and College Union general secretary Sally Hunt said it is "scandalous" that education secretary Michael Gove is planning to break the Conservative's pre-election pledge not to do away with EMA payments.
She urged MPs to consider the "blighted futures of thousands of young people" when they vote on the issue.