The Government's figures on take home pay should be taken "with several tonnes of salt", the TUC has claimed.
TUC general secretary Frances O’Grady said the figures "do not include the effects of tax credits and benefits".
The Institute for Fiscal Studies (IFS) said the Government's figures on take home pay do not reflect what has happened to household incomes overall.
IFS director Paul Johnson told BBC Radio 4's Today programme that although the Government used "a perfectly sensible set of numbers", there were "two problems" that need to be taken into account.
He said: "First, we have other sets of data - the Office for National Statistics publishes an average weekly earnings index. That went up quite a lot less quickly than inflation in the most recent months.
"And of course they are not taking account of reductions in things like benefits which were occurring over the time. So if you are looking at household incomes, that will be different from what's happened to take home pay."
Labour leader Ed Miliband said David Cameron has "shown millions of people he doesn't understand their lives" after the Prime Minister claimed there are "positive signs" that take home pay is rising:
Cathy Jamieson MP, Labour’s shadow treasury minister, said the Coalition's claim that take home pay was rising was based on "highlyselective figures".
The Prime Minister has insisted there are "positive signs" that take-home pay is rising.
An analysis of take home pay figures circulated by the Treasury has suggested all but the top 10% of earners saw a rise last year.
Overall people saw their take home pay rise by a third more than the rate of CPI inflation, currently 2%.