A Line Lead Mechanic describes the events surrounding his Manager's efforts to get him to sign-off the aircraft release of a B757-200; even though a maintenance No-Go item had not been completed.

Narrative

A B757-200 aircraft over-nighted at the terminal at ZZZ. It was scheduled to depart the next morning. The aircraft had a maintenance item assigned to the overnight workload designated as a No-Go item. The maintenance item had to do with the left engine oil tank filler assembly which had failed a functional check the month before. A maintenance item was generated to have the assembly replaced within 50 flight cycles. An AMT was assigned to work that specific item and replace the oil tank filler assembly.After removal and replacement of the assembly; the AMT had informed myself and another Lead Mechanic 'Y' that the vacuum tester; which was required to perform an operational check of the assembly as per Work Card; was not working properly and [was] inoperative. Upon hearing this news; the Manager became enraged and asked myself and the Lead Mechanic 'Y' to persuade the AMT to perform the operational check by alternate means - running the engine (not on the Workcard). We did not agree to do so. Lead Mechanic 'Y' and myself decided it was best to send a Shop Steward out to the airplane with the AMT because we felt that the Manager would begin to put pressure on him to sign-off the item due to the delay probability. Later; myself and Lead Mechanic 'Y' were very busy in the office; closing out other Logbooks; preparing the dayshift workload and contacting AMT's for Overtime. At this point; departure time has passed; and I am now approached by the Manager in my office; at which time he asks me to release the aircraft for Service; as there was a deferral message being sent over the printer from the Manager on Duty for the maintenance item in question. This message would be the authority allowing me to defer the No-Go item. I told the Manager I would not release the aircraft until I had the printed message in hand. The Manager then became very enraged at my refusal to release the aircraft. He began to pressure me and verbally harass me loudly stating; 'I will remember this. I will not forget this. How could you do this to me? Why can't you take my word for this? My word is not good enough for you?'I began to tell him it has nothing to do with trust; and that I would not release the aircraft without the proper deferral authorization. A few minutes later; I was handed the message and I then released the aircraft. Management tell us to be 100% compliant with paperwork and to not release a logbook without all proper documentation; yet they appear to be managing contradictory to the rules for compliance. Maybe Management should be educated on maintaining compliance even if it might cause a delay. Safety and compliance should be first priority for everyone.