Workers on zero-hours contracts are being paid £6 an hour less than other employees, according to research published ahead of a summit to study what action is needed to tackle the issue.
Labour is bringing together unions and employers following the revelation that a million people could be employed on zero hours, under which they are not guaranteed work from one week to the next.
The opposition said official figures analysed by the Resolution Foundation showed that zero-hours workers earned an average of £9 an hour, compared with £15 for other employees.
Labour said the summit, in London, was aimed at discussing the growth in zero-hours contracts and what could be done to tackle their "abuse".
Shadow business secretary Chuka Umunna said: " New evidence highlights that there could be hundreds of thousands more people on zero-hours contracts than previously thought. That's hundreds of thousands of people in insecure work earning far less than average pay.
"Flexibility works for some, but the danger today is that too often insecurity at work becomes the norm.
"The huge spike in the use of zero-hours contracts has brought increased reports of abuses and bad practice. There should be zero tolerance of such abuse.
"That is why Labour has convened this important summit bringing together representatives of employers and employers to consider what action must be taken. In contrast, this Tory-led Government has refused to have a proper and full consultation on the rise of zero-hours contracts or to treat this issue with the seriousness which it deserves."
Business Secretary Vince Cable has ordered a review of zero-hours contracts following growing controversy over their use.
He said: "Since 2005 there has been a rise in the use of zero-hours contracts.
"For some these can be the right sort of employment contract, giving workers a choice of working patterns. However for a contract that is now more widely used, we know relatively little about its effect on employers and employees. There has been anecdotal evidence of abuse by certain employers - including in the public sector - of some vulnerable workers at the margins of the labour market.
"Whilst it's important our workforce remains flexible, it is equally important that it is treated fairly. This is why I have asked my officials to undertake some work over the summer to better understand how this type of contract is working in practice today."
TUC general secretary Frances O'Grady said: "It's hugely concerning that zero hours contracts are becoming such a prominent feature of the labour market.
"Workers on zero hours contracts are completely at the whim of their boss, who can reduce their income to nothing without warning or reason.
"The Government must act to stamp out abuses of workers on zero hours contracts, before the low-pay and insecurity that they bring starts becoming the norm for new jobs."
A study by the Chartered Institute of Personnel and Development found that up to a million people could be employed on zero-hours contracts, four times as many as official estimates.