And many are threatening to boycott the new product.
Vodafone hopes to launch the new e-voucher in the next couple of weeks. But the network is offering a commission which is 0.5% lower than its existing products.
The mobile phone networks have come under fire from retailers for their policy of continually reducing the commission rates offered on all top-ups.
Most retailers now argue that margins have reached the point where they are almost uneconomic.
John Heagney, Nisa-Today’s commercial director, said: “We are seriously concerned about the continued erosion of margins by the mobile phone networks.
“The latest move by Vodafone, with the launch of the e-voucher with another margin reduction, underlines yet another attack on retailers’ profitability.”
Jerry Marwood, managing director of Spar UK, said: “We are very unhappy with this. Why would we accept the new product with its lower retail margin? There’s no incentive.”
And Kenton Lawton, trading director at Londis, said: “While the initiative is good, the margin being offered isn’t.
“We are happy to work with the networks to promote the sale of top-ups but our retailers need to see acceptable margins.”