Kenya has started screening more than 1,600 senior police officers in an effort to weed out corruption.
Anti-corruption commission director Patrick Lumumba told the BBC a committee would check whether the officers had faced corruption allegations.
It would also order the policemen to undergo psychometric and physical fitness tests.
Kenyan police are often ranked as the most corrupt in East Africa.
In 2005, a recruitment drive for new police officers was cancelled after 80% of applications were found to have paid bribes or used their connections to get a job.
The BBC's Anne Waithera in Nairobi says the exercise is the first of its kind in Kenya and is intended to restore public confidence in the police force.
All officers above the rank of superintendent will be screened.
"One of the things we will determine is whether a particular officer has a case or cases that may undermine his ability to serve with integrity," Mr Lumumba told the BBC's Focus on Africa programme.
But Kenya's Central Organisation of Trade Unions (Cotu) said it wanted the process to be suspended because it was not represented on the vetting committee, according to the Daily Nation newspaper.
"If this is not done, the exercise is likely to be perceived to have been conducted by the government with a view to get rid of certain officers within the police force," the union's Secretary-General Francis Atwoli said.
The committee has started the exercise in north and western Kenya.
It is due to extend the campaign to Nairobi next week.