A serving policeman and a former officer are among six men arrested by the PSNI over alleged bribery and misconduct.
Detectives from Serious Crime Branch made four arrests in Northern Ireland and two in England as part of an investigation into the awarding of a number of PSNI vehicle contracts.
The suspects were arrested on suspicion of a range of offences including bribery, misconduct in public office and procuring misconduct in public office.
The four men arrested in Northern Ireland include a 48-year-old police officer, a 37-year-old member of police staff, a 54-year-old former police officer and a 62-year-old civilian.
They were arrested in Antrim, Down and Tyrone and have been taken to the Serious Crime Suite at Antrim police station.
Two civilians were arrested in England, aged 34 and 54, and are being brought to Northern Ireland for questioning.
A number of searches at residential and business premises were also carried out and several items have been seized.
A police spokesman said: "The Police Service expects its officers and staff to behave professionally, ethically and with the utmost integrity at all times.
"Any conduct which brings or is likely to bring discredit on the Service will be investigated to establish whether or not a breach of the Code of Ethics has occurred.
"This may, as a result, lead to a criminal investigation."