Sales were down 29% the week ending March 19 - the lowest in US history.
Revenue from film music, which makes up 80% of IMI members revenue, has come to a halt.
The African streaming giant has seen a recent increase in streaming and subscription activity.
The letter, sent today, was also signed by Anderson .Paak, Gwen Stefani, and Tim McGraw.
Advances granted between now and April 16 will be offered with no fees or interest of any kind for the next year.
The music veteran is currently undergoing treatment at the UCLA Medical Center.
Green Day, ASCAP, Stormzy, Coachella and SXSW have all been axed or postponed due to Coronavirus fears.