In my case I've defined a Quote template that insert a line that contains a product : 'Timbre fiscale' it include a tax  price= 0.6 that must be add one time on each invoice.
so when i decided to creat an invoice for multiple sale order this line has been repeated the same way as the numbre of the sale orders, 

can you suggest for me how can I avoid this, i want to remove the extra lines and keep only one when  I  create  an invoice for multiple sale order