Rail workers in California are to face psychometric tests following the takeover of the five-county Metrolink system by Amtrak.
The new operating contractor has introduced the psychometric tests in an effort to gauge the suitability of job applicants.
Southern California's commuter rail service engineers and conductors are required to undergo a new personality-profiling test following the 2008 Chatsworth disaster, in which 25 people were killed and 135 injured.
Although the move has been widely welcomed, the introduction of psychometric tests has resulted in a dispute between staff and management and unions for engineers and conductors have threatened to boycott the tests.
The main cause of the clash is news that the new Metrolink-Amtrak agreement requires that even experienced crew members - who have worked on the network for years - must also undertake the tests.
Meanwhile the Metrolink board has shown its concern for safety following investigations that found that engineers had repeatedly violated safety norms prior to the Chatsworth catastrophe.
According to board member Richard Katz the aim of the psychometric tests is to assess the caliber of the existing workers only, it has nothing to do with shunning out the failed workers.