A delivery firm listed on London's Alternative Investment Market (Aim) is under investigation by London police.
DX Group said an allegation against the company has resulted in a preliminary investigation centred on the DX Exchange operations, its collection and delivery service.
"The investigation is at a very early stage," DX said in a statement.
DX, which supplies the majority of the top legal firms in the UK as well as central and local government, banks and accountants, did not give any details on the allegation.
The firm said its board received details of the allegation on 7 June and was co-operating fully with London police's economic crime directorate.
DX earlier this week won the backing of activist investor Gatemore Capital Management after it revised terms for the proposed merger between DX and John Menzies' distribution division.