Almost 300,000 workers in the South West are "under- employed" – an increase of 34% since the start of the recession – according to a union study.
The TUC said around one in eight workers (293,600) in the region are doing part-time jobs because they can't find full-time positions.
The region has the highest rate of part-time employment at around one in three workers.
It also has one of the highest rates of self-employment, thought to be part of the reason for a growth in under-employment.
Nigel Costley, regional secretary of the South West TUC, said: "Unemployment is a major problem across the South West. But this only tells half the story.
"Nearly 300,000 people are trapped in jobs that don't have enough hours to provide the income they need to get by. Fewer hours mean less pay, and an even bigger struggle to pay the bills.
"Young people, women and low skilled workers are bearing the brunt of our under-employment crisis. It is alarming just how few young people today are able to find a job working enough hours.
"This is a criminal waste of the talent and skills they have – all because of a crisis they didn't cause."
The TUC found that about one in ten workers across the UK are under-employed, though the likelihood of being affected varies considerably by age, gender and job sector.
Women are more likely to be under-employed than men, with around one in eight employed women finding themselves without enough hours.
Low-skilled jobs are worst affected, with some one in five workers not getting enough hours. Young people are almost twice as likely to be under-employed as any other age group.
While the TUC said "any job is better than no job at all, particularly during a recession" it said it was concerned that under-employment is becoming an ever-more permanent feature of the labour market. "Long periods of under-employment can do permanent damage to people's careers," Mr Costley added. "Ministers need to start taking the issue seriously as it's dragging down the economy as well as causing financial hardship.
"Solving our under-employment crisis is not easy, and it won't be tackled through endless unpaid work initiatives.
"What the country needs is an economic strategy that puts people's futures ahead of self-defeating austerity.
"Cuts in infrastructure spending must be reversed and growing industries need more government support. We also need banks to start lending again, so that businesses can grow and create jobs."