Protesters have been mailing empty packets of crisps back to Walkers – but Royal Mail have issued a reminder to use envelopes.
The campaign has been launched with the aim of protesting the non-recyclable nature of the plastic crisp packets.
And people have been encouraged flooding social media with pictures of them putting the empty Walkers packets in post boxes – in a bid to put pressure on the company to change its packaging.
In a guide published on social media, protesters are encouraged to stick the Walkers freepost address on the empty packets and then put them in post boxes.
The Royal Mail are obliged to return the empty bags to Walkers freepost address - but is now telling people to stop posting them without envelopes
Because the crisp packets are not being sent in envelopes they cannot go through the Royal Mail's sorting machines - and have to be done by hand, creating more work for staff.
A Royal Mail spokesperson told the BBC: ‘We strongly encourage customers not to post anything into the postal system which is not properly packaged.
‘Crisp packets can't go through the machines, they are not normal mail items therefore my hardworking colleagues need to manually sort them, which adds to time.’
A petition was launched by 38 Degrees calling on Walkers and other crisp manufacturers to ditch the plastic bags.
On the petition, which has racked up 310,000 signatures, Geraint Ashcroft wrote: ‘Currently the majority of crisp packets in the UK and Worldwide are not recyclable so they have to go to landfill.
‘As a nation the UK alone consumes approximately 6 billion packets a year. Imagine what the figure would be for Europe or Worldwide.
‘That's an awful lot of landfill and poison for the environment.'
Walkers has committed to making all its packaging 100% recyclable or biodegradable by 2025.
However campaigners want the company to make the change sooner.