Ukip general secretary Roger Bird has been suspended by the party over allegations relating to candidate selection.
Ukip said it has launched a "full investigation" into the claims of impropriety but has not said what the allegations relate to.
It is not believed to be linked to the recent departure of more than a dozen Ukip activists who quit the party over leader Nigel Farage's handling of the candidate selection process.
A Ukip spokesperson said: "Shortly after a claim came to light about the conduct of Mr Bird with regard to candidate selection, the UK Independence Party took action swiftly and decisively, including steps involving external human resources consultants, as well as following due process and the party's constitution to the letter."
"Unfortunately, Ukip has had to suspend Mr Bird pending a full investigation into allegations made against him. The party has acted swiftly and decisively and will not tolerate impropriety of any kind amongst its staff."
A former Conservative councillor in Wandsworth, south London, Bird quit the Tories in 2009 and switched to Ukip a year later. He was named last year as Ukip general election candidate in the Surrey constituency of Mole Valley.