Almost four out of five Public and Commercial Services (PCS) union members did not feel there were enough staff and two thirds said they were frequently asked to work overtime, said the union.
It has long been obvious that staff are under-resourced and under-trained and that universal credit is at risk of collapse. The DWP cannot keep burying its head in the sand and hope these problems go away because they are only going to get worse if nothing is done.
More than half said they did not think Universal Credit was an improvement for claimants.
A Department for Work and Pensions spokesman said: "The PCS survey comprises of only 13% of our 2,700 staff working on Universal Credit. They chose to ignore staff in our Jobcentres when conducting this research providing a skewed unrepresentative sample of union members."
A study has found that Universal Credit, one of the Government's flagship policies, is in "disarray", suffering from a lack of staff, poor training and inadequate IT.
A survey of around 400 members of the Public and Commercial Services (PCS) union showed that 90% believed expensive IT systems dealing with the benefit were less than adequate. Almost three quarters said working conditions were worse than in their previous role and four in five said the training was less than adequate to prepare them for working on the scheme.
Iain Duncan Smith has defended the Universal Credit scheme, claiming it is under budget and helping people find work quicker and earn more.
The flagship scheme - which merges existing income-based benefits such as Jobseekers Allowance (JSA) and tax credits into a single payment - is due to be rolled out across the country tomorrow.
The Work and Pensions Secretary denied claims the flagship scheme was over budget, insisting his department was spending £600 million less on the programme than expected.
Speaking on the BBC's Andrew Marr Show, he said Government research showed that those receiving the benefit were 5% more likely to find employment within four months than comparable JSA claimants.
Labour said the scheme was massively behind schedule and saving far less than expected, describing the roll-out as a "spiralling waste and delays".
Labour have said the Government is falling far short of the numbers of people it said would be moved on to the new Universal Credit scheme.
Chris Bryant, shadow welfare reform minister, said: "Iain Duncan Smith has repeatedly broken his promises on Universal Credit. He promised a million people would be claiming Universal Credit by April 2014, but the latest figures show fewer than 15,000 people are claiming the new benefit.
"Today Iain Duncan Smith promised 100,000 people will be on Universal Credit by May 2015. But that's only around 1% of the total number of people who are expected to claim the new benefit."
A new government report suggest trials of the Universal Credit welfare reform show it is on track to help people into work.
The study from the Department for Work and Pensions found those on the scheme were working more over a six-month period, while two-thirds said it offered better incentives to work.
The department says the scheme will deliver £35bn in economic benefits over 10 years after it is fully implemented.
The new credit is still in its early stages and will be available in over 90 job centres by this Christmas.
Work and Pensions Secretary Iain Duncan Smith said: : "Universal Credit will help people into work more quickly and help them to earn more, giving people the confidence that work always pays, along with the economic security of a regular pay packet."
The Government's Universal Credit programme will roll out across more JobCentres from the beginning of next week.
The new payment, which combines six means-tested benefits and tax credits into one benefit, will be expanded across the north-west of England.
The latest figures show that up to March of this year, 6,550 people had claimed Universal Credit.
Iain Duncan Smith's universal credit scheme has been given a unique classification in an annual progress report issued by the Government.
Although many of the projects are listed as being "exempt" from publishing a green, red or amber risk (most citing the Freedom of Information Act as the reason), the universal credit scheme is the only one to be listed as "Reset".
During 2013, the Programme was reset, culminating in the revised plans announced on 5 December 2013.
The lack of transparency was highlighted by The Independent, which claimed the Major Project Authority had rated universal credit as “red”, signifying that it is “unachievable within reasonable timescales and to a reasonable budget without urgent remedial action”.
Iain Duncan Smith has successfully prevented the publication of a "damning" report into his universal credit scheme, according to The Independent.
As part of its drive to increase transparency, the Government published the progress of around 200 projects today, rating each on a risk scale of green, red or amber.
But today's Independent front page claims universal credit was "the only project not to get a rating".
The progress report represented £400bn of public spending.
The Government dismissed claims it had deliberately obstructed an inquiry into the botched roll out of their flagship Universal Credit reforms.
A spokesman for the Department of Work and Pensions said:
Universal Credit and its IT systems are very clearly working well, with claimants receiving the new benefit and moving into work.
We deliberately started in a slow, controlled and safe way, which the Committee itself has long recommended, so we can expand Universal Credit securely to more people.
Universal Credit is on track and we will start expanding it to other Jobcentres from this summer.
We have made our plans to roll out Universal Credit very clear with regular updates.
MPs have expressed scepticism about the Government's ability to deliver wide-ranging benefit reforms on time.
The Work and Pensions Select Committee said Iain Duncan-Smith's department had worked at "a snail's pace" and failed to be open and transparent with their investigation.
Whilst it is right to ensure that the system works properly before extending it, there is a difference between cautious progress and a snail's pace.
Given the excruciatingly slow pace of roll-out to date, it is hard to see how the most recent implementation timetable can be met.
Effective select committee scrutiny depends on the provision of accurate, timely and detailed information by government departments.
DWP has not always provided this to the committee in the case of Universal Credit.