While those in the highest pay bracket have enjoyed an increase in their wages amounting to more than £4200 a year, the bottom 10% are struggling to find the working hours they need to make ends meet.
Hit with a substantial decline in their take-home pay, those in low-paid jobs such as cleaners face an uncertain future unless action is taken to reverse current trends, the STUC, which produced the report, has claimed.
Stephen Boyd, assistant secretary of the Scottish Trades Union Congress, warned of an urgent need to address the growing gap between those at the higher end of the pay bracket and those at the lowest, revealed in the organisations 2014 Budget Submission.
He said: "We really need to think about what the growing number of poorly paid jobs means to us as a society - is this the way we want to go?
"Unless you address the labour market failures at both ends of the spectrum, where those in the very upper echelons are able to control the labour market in a way that means it doesn't function as a market at all and they can pay themselves what they want, while those at the bottom are left to scrape by on too few hours on a minimum wage, you are never going to address inequality.
"Now is the time for politicians to grasp that. If they don't, we are going to see these trends become further imbedded."
Overall, the bottom 10% of the 70,000 workers in elementary occupations, such as cleaners, have seen their wages fall by 14.8% between 2009 and 2013 before adjusting for inflation.
The bottom 10% of the 180,000 workers in elementary administrative service jobs, such as postal workers and hospital porters, suffered a nominal decline of 9%.
As the minimum wage - currently £6.31 for over-21s - protects workers, it appears wage falls are driven by cuts in working hours.
Meanwhile, the top 10% of corporate managers and directors enjoyed an increase in gross weekly wages of £82 per week, or £4290 a year.
Boyd said the Scottish labour market was becoming a "more insecure and unwelcoming" place where workers could not be guaranteed security.
Boyd said: "We have seen the labour market over the course of the last six years react to the fall in economic output very differently than it has in previous recessions, so unemployment never reached as high a level as we might have expected.
"But what we have seen beneath that is a huge rise in under-employment and people not able to find enough hours to make ends meet."