How can deletion of attachments be restricted after the invoice has been submitted for approval?

Organization Name (Required - If you are an Oracle Partner, please provide the organization you are logging the idea on behalf of):

LOLC Technologies Ltd

Description (Required):

Attachments can be deleted after the invoice has been submitted for approval.
Are there any controls or workarounds to restrict this?

Use Case and Business Need (Required):

Enhancement Request / Service Request: Enhancement Request