Mailing houses have accused the postal operator of trying to "hijack" advertising space on the front of envelopes and one-piece mailers to promote its own business.
Equally controversial is the fact the mark will be applied to all letter format items that pass through Royal Mail's automated sorting machines, including mail that has originated from downstream access (DSA) providers.
A formal complaint was lodged with Postcomm by the DMA yesterday after Royal Mail gave the industry just two months' notice of the specification change.
Alex Walsh, head of postal affairs at the DMA, said: "The timescale is a nonsense. People have designs, they have campaigns planned, direct mail doesn't happen overnight.
"What are businesses supposed to do with things like stocks of pre-printed envelopes - junk them? Or just accept that there's going to be a Royal Mail mark overprinted on their logo, which will look a right mess? I would say the absolute minimum is that you ought to be giving people six months' notice."
While other elements of the MDS are based on operational requirements, the purpose of the new mark is purely to advertise Royal Mail's role in final mile delivery.
"There is a big difference between putting a mark on which means letters are processed and delivered more efficiently and sticking your own promotional messages on - it does seem to be overstepping the mark," said Walsh.
"If they are changing the specification and changing the terms under which they are going to supply these products, we believe that that is a breach of their licence if they haven't actually gone to the regulator and sought permission."
A Royal Mail spokesman dismissed the criticism, saying "current legislation does not require us to consult on this"; however, mailing houses said this was typical of Royal Mail's "arrogant" approach.
The spokesman added: "The space we have designated for the mark is the least likely to be used for return addresses or any other form of artwork. We will be notifying customers to make them aware of the mark we will be printing so that they can avoid printing messages in the same area if necessary."
Walsh said: "This seems to be saying: we have the right to do whatever we want with this envelope. I think many people would see that that is theirs and not Royal Mail's to do whatever they want with."
