>>A few Chief Pilots are infamous for phoning a pilots present employer and asking for an unnoficial reference<<
A completetly self defeating attitude. It soon gets round that this practice is in hand and pilots are put off applying to the host airline.
Why? Because is you know that, prior to accepting a acontract your present Boss is approaches informally then you will save yourself the trouble in the first place.
Ever wondered why sone airlines have problems getting pilots despite the money?
There is a proper time and place for references.