A friend of mine received in the post while out sick a warning from his employer about the amount of days he has taken due to sickness.This is his first warning in the job where he has worked for over 20 years, He does not know whether to write back to this letter. He has supplied doctors note when required.Should the employer have rang him first or asked him in for a meeting,he feels he is been bullied to get back to work.He is not in a union any advice appreciated.What should he do next as he is due back to work this week.