The Scottish Government has been accused of failing to sufficiently focus on the type and quality of jobs being created in its economic strategy.
The Scottish Trades Union Congress made the claim at Holyrood to MSPs investigating the problem of underemployment.
In 2011 there were 204,200 workers who wanted extra hours in their current post, the STUC said.
Underemployment can also include those not utilising the skills they have in their existing role.
Stephen Boyd, STUC general secretary, is to be questioned by MSPs on Holyrood's Economy Committee about the problem.
In a submission to the committee before the meeting, the STUC said it "believes that the Scottish Government's current economic strategy, like its predecessors since devolution, gives insufficient weight to the nature and quality of jobs created".
Underemployment is not a new concern, the submission said. "Prior to the recession too many Scottish workers were unable to find jobs which provided sufficient income or maximised their skills," it said.
If and when the economy has recovered fully from the recession, the problem may have become embedded, with companies continuing to rely on temporary and part-time staff rather than taking on new workers, it also warned.
"While underemployment has helped sustain better than expected headline employment during the prolonged downturn, the opposite is likely to prove true during any recovery as firms utilise hoarded and part-time, temporary labour or re-establish normal overtime arrangements to meet new demand, rather than employing additional workers."
It is "unequivocal" that, in the short-term, the best solution for underemployment is government stimulus "to help increase the demand for labour", the STUC said. "Longer-term solutions must look to grow the number of full-time, quality job opportunities in the Scottish labour market."