Research for the single parent organisation Gingerbread found that moving to the Universal Credit, a new system of a one-off monthly payment, will affect working parents.
The plan is for Universal Credit to replace income-based Jobseeker's Allowance, income-related Employment and Support Allowance, Income Support, Child Tax Credits, Working Tax Credits and Housing Benefit with just one credit, with the aim of ensuring claimants are always better-off taking work.
Gingerbread said its research showed those taking part-time jobs would be slightly better off, but if they worked more than 20 hours they would struggle to make employment pay.
Glasgow South West MP Ian Davidson said the research showed the planned changes would not benefit people who want to work.
Of the seven Glasgow parliamentary constituencies the number of single parents is well above the national average.
Glasgow East has the highest in Scotland at 47%, with Central on 45% and North West 43%.
South West and South each has 39%, while Glasgow North has 36% and North East 31%.
The study says the average income of a single parent will be £3.43 a week lower under Universal Credit, while for all families it will increase by £2.16. Single parents on the lowest incomes will lose out by more than £5 a week.
Middle income earners will lose less, while those at the higher end will lose more (£6.61) due to changes that will see the removal of child benefit.
According to the research, non-working single parents will also have lower incomes following the changes.
Gingerbread says the research shows the claim that reforms will make work pay are not true.
Chief executive Fiona Weir said: "It's worrying to see that single parents will, on average, be worse off under Universal Credit than they are now. In the current difficult economic climate any new reform to the system must make lives better for families, not worse".
Mr Davidson said: "These findings about the impact on single parents should be a wake-up call for the Government.
"Single parents in my constituency tell me they do want appropriate work that pays, but that they are often confounded by a system that does not meet their particular needs.
"Whilst the Prime Minister tells us it is great news the workforce is increasingly flexible, there is a serious risk people who have fixed commitments to work around, such as single parents, are being put in an impossible situation."
The Credit is due to be fully operational by 2017 and has been trialled in some areas of England, but has not started in Scotland.
A DWP spokesperson said: "Universal Credit will make 3m households better off and lone parents will on average gain £5 a month.
"Around 500,000 working lone parents will see a greater incentive to increase their working hours and for the first time they will be able to have help with childcare even when they are working for just a few hours."