UPDATE Trigger on multiple tables

Is it possible to have a single trigger on multiple tables 
simultaneously? Example:

CREATE TRIGGER emp_cust_stamp BEFORE INSERT OR UPDATE ON employees, customers   FOR EACH ROW EXECUTE PROCEDURE
last_updated_stamp();

I tried something like the above but get an error message at the comma. I tried using the keyword AND as well. 
I couldn't find anything on this in the docs. I have many different tables in my databases which all have a 
"last_updated" field and it seems less tedious to be able to enforce updating this trigger database-wide using 
just one trigger. Is it possible?

Ferindo