The imminent arrival of the national living wage has been criticised for not going far enough to drive up pay rates.
TUC general secretary Frances O’Grady said the introduction of the new national living wage from this Friday was a welcome move.
However, she said the new structure let down tens of thousands of workers based on nothing more than their age.
She also said the apprentice rate of £3.40 did little to encourage young people to learn a trade.
“The TUC fully supports a higher minimum wage,” Ms O’Grady said.
“However, we don’t think it’s fair that under-25s will be on a lower hourly rate. They face many of the same expenses as other adults and should be paid the same.
“If the Government wants to attract more young people into apprenticeships, it needs to up the £3.40 apprenticeship rate. Future minimum wage increases must do more to narrow the pay gap between old and young.”
The new rules mandate a minimum payment of £7.20 per hour 50p more than the current national minimum wage for all workers over 25 and not in the first year of an apprenticeship.
Failure by an employer to pay the national living wage could result in a number of sanctions being taken against a business including being forced to pay back arrears immediately, a financial penalty, and being named and shamed by the Government.
Resolution Foundation research estimated 500,000 Scottish workers will be in line for a pay rise come Friday.
The immediate impact varies around the country, with an estimated 18% of Dundee workers due an increase, a similar level to that in Aberdeen, Edinburgh and Glasgow.
However, almost a third of workers in Clackmannanshire will benefit.
The hospitality and healthcare sectors are expected to feel the changes most, as many workers are traditionally on lower-pay scales.
Research has suggested a third of employees do not check their payslips, but Stewart Gee of conciliation service Acas urged workers to brush up on the changes to ensure they were being treated fairly.
He said: “Eligible workers should check what they are entitled to under these new changes, and employers need to ensure that they are ready, too.”
The imminent introduction of the new wage structure has led to concerns that firms will cut overtime and bonus payments in order to keep costs low whilst complying with the legislation.