Citizens UK said the employers of five million workers in the UK were being "subsidised" by the taxpayer.
The minimum wage is £6.50 an hour for people over 21, while the living wage calculated by the Living Wage Foundation is £7.85 (£9.15 in London).
The British Retail Consortium said most supermarkets paid above minimum wage.
When all extra earnings were considered, hourly pay was around £8.40, it added.
According to Citizens UK, which organises community campaigns, most of those earning less than the living wage are employed in the retail sector.
The charity said this meant most supermarket staff needed in-work benefits - which it argued meant taxpayers were "subsidising private companies by almost £11bn per annum".
Supermarket workers paid the national minimum wage are forced to claim state benefits totalling £11bn a year, according to a charity.