Britiain's 5.2m low-paid workers include many of the 760,000 retail sales assistants employed in UK shops.
Employers say many receive other benefits such as discounts, while critics says 'in work' benefits paid for by the taxpayer to up minimum wage to a 'living wage' should be paid for by the employer.
The national minimum wage will increase by 20p an hour to £6.70 from October 2015.
The changes will benefit more than 1.4 million workers.
The hourly rate for younger workers will also rise, and for apprentices it will go up by 20 per cent - or 57p - to £3.30 an hour.
The rates were recommended by the Low Pay Commission.
Labour leader Ed Miliband has promised in the Labour manifesto the minimum wage would rise to more than £8-an-hour by October 2019 under a Labour government.
Wylie said: "It's difficult to say the impact. There's a big difference between 10p an hour and £1 an hour extra, and there's regional variations and market rates.
"One one level, if you want quality staff you have to have a reason for them to join and if you're at the bottom of the pay scale and you can get more money cleaning toilets then it's difficult.
"Members have different views but my personal view is I'm not sure there is as big an impact as everyone thinks. If you make the minimum wage the living wage then the living wage will go up."