CARE's Taxation of the Families report found the tax burden on one-earner married couples on an average wage with two children is 26 per cent greater than the OECD average and 17 per cent greater than the EU average.
In comparison, the tax burden on single earners on the same wage is 8 per cent less than the OECD average and 19 per cent less than the EU average.
In addition, CARE found married single-earner families earning between 50 per cent and 75 per cent of the average wage were even worse off tax-wise.
It found they only take home 27p in every pound once income-based taxes and national insurances are taken into consideration.
In comparison, poorer one-earner families in the rest of the OECD take home 66p in every pound once income tax and other national insurances are considered.
CARE has argued the best way to reduce the tax burden on one-earner families is to allow the non-earning partner to transfer more of the amount they can earn before tax kicks in to their earning partner - effectively giving them a tax break.
Currently non-earning spouses can only transfer 10 per cent of their personal income allowance to their partner, but CARE says they should be able to transfer all 100 per cent of it.
Conservative MP and Christian Fiona Bruce said: "It is particularly concerning that at present more marriage tax relief is afforded couples in their 80s and 90s, whose children will have left home long ago, than on all other marriages including those caring for young children.
"Whilst we should of course care for our elderly, we should give a significant married tax break to young families who also need our help."
A Her Majesty's Treasury spokesman said: "We're committed to recognising the importance of marriage in the tax system. That's why we introduced the Marriage Allowance, which has already helped over 1 million families across the UK cut their income tax bills by over £200 a year.
"Our planned increases in the personal allowance will make the Marriage Allowance more generous every year."