Q. Do you issue or raise an early warning?

A. Neither of these. Assuming this is NEC3 ECC, clause 16.1 requires the Project Manager (PM) or the Contractor to give an early warning by 'notifying' the other as soon as blah blah. All either party needs to do is fill in a very simple communication form (such as those produced by NEC) that says eg 'Under clause 16.1 I notify you that a Subcontractor may be going insolvent/a supplier may be delivering some key Plant and Materials later than promised/the Employer has requested we change the permanent fencing layout (yet again!)/a protest group has threatened to invade the Site....' and so on. The contract does not ask either party to say anything more than stating the matter itself that is giving concern - it does not say fix it, or somehow rank it, or submit proposals or anything other than what is it, and this needs to be properly communicated via a notification. Use the NEC Project Manager's notification form or the Contractor's notification form. PMN or CN if you like acronyms. Simples. So again, this is about properly and closely following what the contract requires you to do, no more, no less. Follow the language. Follow the processes.