hi
builder seems to want to get ahead and some tiling shop workers have no idea about tiling.
the problem is everybody wants to be done and paid and wants it done quickly,dont give in as it will be you getting the call when the tiling fails and it will be your time and money fixing it. do it right the first time and if the builder doesnt like it then tough atleast you know your doing it right. i had trouble with plumbers last week as they had installed the undertile heating sensor and thermostat before id even layed the insulation boards,i made them remove them and they moaned at me and asked if i always did things by the book,thought everybody did,apparantly they dont!!!
good luck and you cant go wrong with the advice from everybody above,sand it off,prime it and id use a powdered adhesive and you'll have no problems.