(Corrects final line to show unions have to give 48 hours notice of strike, not give notice within 48 hours of certificate)
JOHANNESBURG, Nov 20 (Reuters) - A strike certificate has been issued at South African airline Comair as part of a secondary strike against South African Airways, a spokeswoman for the National Union of Metalworkers South Africa said on Wednesday.
Two unions that called a crippling strike at SAA said on Sunday they would pursue a secondary strike to ensure their demands are met, that they warned could shut down the entire aviation sector.
After a strike certificate is issued, unions have to notify employers within 48 hours of any strike action. (Reporting by Emma Rumney; Editing by Catherine Evans)