Two BP rig supervisors and a former executive pleaded not guilty on Wednesday to criminal charges stemming from the 2010 Deepwater Horizon rig explosion and Gulf of Mexico oil spill.
Well-site leaders Robert Kaluza and Donald Vidrine are charged with manslaughter in the deaths of 11 rig workers.
They are accused of disregarding high pressure readings before the well blowout.
Former vice-president David Rainey was charged separately with concealing the level of the oil leak from Congress.
BP announced earlier this month that it will plead guilty to manslaughter, obstruction of Congress and pay a record $4.5 billion (£2.8bn) in fines.
As Aslef's annual assembly of delegates begins in Edinburgh tomorrow the general secretary explains the challenges his members - and workers across the country - face