Young people job-hunting or planning to continue in education have been warned they are facing the toughest outlook since 1994.
The TUC has voiced concern over rising levels of long-term unemployment, accusing the government of cutting financial support for students.
In a report published ahead of new unemployment figures on Wednesday, the union said the proportion of young people in full-time education has almost doubled from 24% in 1992 to 41% this year, the Press Association reported.
More than one in five people aged between 16 and 24 were out of work, significantly higher than in 1992, when the rate was 16%, said the report.
Prospects for young people deteriorates sharply when the recession started in 2008 and have been at "crisis levels" ever since, the TUC warned.
Almost half a million young people have been out of work for at least six months, leaving them under-achieving before their careers have even started, said the TUC.
General secretary Brendan Barber said: "Students looking to start their careers or continue in their education next month are facing the toughest climate for nearly 20 years.
"It's particularly worrying that long-term joblessness for young people is still rising, even as overall unemployment falls. If this continues we could lose a generation of talented and highly qualified youngsters to blighted careers, debt and under-achievement."
In July, the government announced private companies would be paid to wake up teenagers in the morning in a drive to get more youngsters back to work, as part of Nick Clegg's Youth Contract.
But Barber added: "Ministers should be doing everything they can to help young people but so far all they've done is cut vital financial support for college students and price people out of university. Jobs support has been scrapped, scaled back and then reinstated on the cheap. This is no sensible way to help young people into work or education.
"The government's economic strategy is holding young people back. It's time for a new plan that invests in their futures, rather than stunting careers before they've barely begun."
Unemployment fell by 65,000 between March and May to 2.58 million, although the number of people claiming jobseeker's allowance in June increased by 6,100 to 1.6m.
Figures released in May revealed half a million people were unable to move from education into employment, raising concerns they were being "shut out" from the job sector.
As students in England, Wales and Northern Ireland prepare to receive their A-level results on Wednesday, a survey by the National Union of Students showed that three out of four youngsters intending to go to university this autumn are worried about getting a job after they finish their course.
The poll of 800 students also revealed that around two thirds had concerns about finances while they studied.
NUS vice president Rachel Wenstone said: "For many people, a university degree has traditionally given them the opportunity to access the employment of their choice. Now those who make it to university are no longer guaranteed employment in the way that previous generations were.
"Unemployment amongst graduates is still lower than for those without a degree but those getting their A-level results this year face harder decisions than many about their futures.
"The government's disastrous reforms to university funding mean that many prospective students must choose between taking on thousands of pounds in loans to pay for an uncertain future, or taking their chances in one of the most hostile jobs markets anyone starting a career has faced."