How to remove Sales, Service or Sales Contract from To Be Invoice status

Dear All,

I am BYD customer.

In my Customer Invoicing Work Center I get hundreds of Invoice Request which consists of below Document Types

1. Sales Order
2. Service Order
3. Sales Contract
4. Service Confirmation
5. Outbound Delivery
6. Manual Invoice Request   & so on

I don't want first three Document Types to come in To Be Invoice list category.

Please suggest...

Regards

Vishal Kambare