I'm amazed nobody has mentioned that LIFO (in the UK and Europe by who we are now ruled) is widely considered amongst the legal fraternity to be highly suspect in terms of its legality because of the age regs. The argument goes that if you are last in you will on average be younger and hence getting rid of those last in is age discrimination. The same applies if you have more female pilots employed relatively recently, only now it is sex discrimination. The same goes for allocating places on a seniority list by date of birth when pilots join on the same day - this definitely would be direct age discrimination in the UK and some airlines have moved to "names out of a hat" as a result, as even hours/experience can also be considered to be indirect age discrimination.
For this reason many UK airlines are attempting to pre-empt a legal challenge by agreeing redundancy matrices that are based on more than just date of joining. They variously include disciplinary "points", training qualifications, etc. They have yet to be tested in court in an airline context but Rolls Royce vs Unite was the catalyst for these changes.