Signs have been put up on Shields Pier pleading with visitors not to do the dirty.
The notices have been put up by the watchmen after a series of incidents where human excrement has been left behind and had to be cleaned up.
The Port of Tyne has confirmed the signs are genuine and also said there has been an issue with people urinating while on the pier.
It has warned the police will be called in to take action if the problem continues.
The sign, signed by the security manager, says: "In recent weeks the pier watchmen have discovered human faeces on the pier on several occasions.
"The watchmen have picked up the excrement, which places the health and safety of our watchmen and public at risk.
"This must stop immediately.
"Anyone caught carrying out such acts will be removed from the pier and banned immediately.
"Please respect our environment and keep the piers a pleasant place to visit.
"Thank you for your co-operation in this matter."
A spokesperson said: "The Port of Tyne is the proud custodian of Tynemouth and South Shields Piers.
"Regular maintenance of around £300.000 each year ensures we are able to open the piers to the public.
"Fouling on the piers will not be tolerated, and we are working with Northumbria Police Neighbourhood Team to monitor the situation and take action where appropriate."