According to The Liverpool Echo, during a visit last week to the Liverpool Institute of Performing Arts, McCartney told the students, "Sometimes the situation in the world is so crazy that you've got to address it."
The song the Beatles legend has written will pertain to President Trump, said The Hollywood Reporter citing The Liverpool Echo's report.
McCartney is a co-founder of the institute, also called LIPA, and was a student there when it was known as Liverpool Institute High School for Boys.
He didn't elaborate further on the song according to the report.
The list of musicians who have sung or tweeted against Trump includes Fiona, Death Cab for Cutie, Roger Waters, Joan Baez, Carole King, Loudon Wainwright III, Billy Bragg and Lady Gaga, among others.