Ukip's free post address has already been targeted by people sending overly-heavy items at the party's expense but it seems one package was the final straw.
A delivery of faeces has prompted the closure of the service.
What kind of person sends faeces or blood to a political party? Are people OK?May 3, 2014
Freepost lets someone send a letter or parcel without a stamp as the cost is borne by the recipient.
Many people have been sending bricks, bottles of water and other heavy items all at Ukip's expense.
Nigel Farage said on Sunday his party will adopt a different approach to tackling claims it is racist with a new election campaign strategy featuring black and ethnic minority candidates this week.
The Ukip leader insisted his party would get on the front foot as it fights against claims of racism, as a poll showed some 35% of people felt while the party is not racist, it "does seem to attract some candidates or supporters with racist, extreme or odd views".
More than a quarter of those polled by YouGov said Ukip was a party with "racist views" and "many racist members".