The TUC says there is a lack of full-time jobs
The UK jobs market looks "deceptively healthy" because of an increase in the number of people having to settle for part-time work, the TUC has warned.
The union body says thousands of people are only taking part-time or temporary work because they are failing to find full-time employment.
Also, an Office for National Statistics report showed a rise in "underemployed workers" working less than they wanted.
The latest UK unemployment figures are released on Wednesday.
The official data for the three months to December is expected to show the UK unemployment rate remained at or around the 7.8% level.
'Not good news'
"Job statistics could be making the market look deceptively healthy - a closer look suggests that thousands of people are taking part-time or temporary jobs because they cannot secure full-time positions," said TUC general secretary Brendan Barber.
"A growth in insecure and low-paid employment at the expense of secure work is not good news for them or for the economy."
The Office for National Statistics revealed on Tuesday that there was a rise last year in the number of underemployed workers.
It said the number of underemployed people rose to 2.8 million in July to September of last year, compared with 2.1 million two years earlier.
Last month's unemployment data showed that total unemployment fell in the three months to November by 7,000 people to 2.46 million.
This was the first fall in unemployment for 18 months.
Most analysts expect another small fall in unemployment for the three months to December.
The Federation of Small Businesses (FSB) said this week that taxes were preventing almost three out of five small firms taking on more staff.
Following its survey of 10,000 small companies, it said it was calling on the government to introduce a cut in national insurance contributions.
"What the UK economy needs is real action to get more people into work, especially under-25s who make up a large proportion of those currently unemployed," said John Wright, chairman of the FSB.