The Royal Mail has warned staff to not accept Christmas tips or gifts valued at more than £30 for fear of bribery charges.
The organisation's My Royal Mail website, under the heading Christmas and the Bribery Act, said: "It's the season of goodwill. But it's important to be careful about accepting gifts so you don't fall foul of the Bribery Act."
It said Christmas tips were allowed but should never be accepted in return for favours.
"A bribe is not just about money, it could be any gift, hospitality or favour," it also said.
Under the heading 'other guidelines' it advices staff to reject gifts worth more than £30.
"Gifts may only be given or accepted up to a value of £30; any gifts over £30 must be politely declined," it said.
Royal Mail spokesman Ian McKay said for many years postmen have been able to accept Christmas tips.
"It is entirely up to customers if they wish to give a tip to postmen and women at Christmas and to what value," Mr McKay said.
"Like all other major companies, we take the Bribery Act very seriously and have a duty to clearly communicate to all of our staff what it means for them.
"We have made it absolutely clear to our people that Christmas tips are allowed."