Not sure if this is a tangent or not.
But we have SEDEX / SMETA ethical audits a lot in the UK and things like the modern slavery act puts more ethical transparency requirements onto suppliers wherever they are in your supply chain. So depending on where your customer is, they may have a different view on what is needed for code of conduct.
I went to a sit though who were struggling after a recent audit. You would not believe the lack of due diligence this (large) company had not done with their suppliers and how little knowledge there was in the procurement team about ethics. What was the problem? Not a random supplier half way across the world but on site contractors. Security, agency staff, cleaning / sanitation, canteen staff. Working beyond the working time directive in the UK (48 hours not including breaks), paying no overtime, not paying according to contracts, making staff pay for workwear etc.
It was the suppliers that the client didn't see as suppliers in the traditional sense who were the problem.
All those contracts procurement were slapping each other on the back for because they were cheap weren't so cheap when they had to increase staff pay. Couldn't have been more pleased to be the one to force that to happen if I'm honest.
Anyway, my point being that "code of conduct" is as long as it is wide and vastly depends on your customer base, the markets you're supplying to etc. I would be super clear what you're expecting someone to sign up to both for the signatory and the procurement team (who should, after all, be the ones driving this not you). Because if the procurement team don't know the ethical, legal and moral requirements of your business, they'll pop some work out to Bob who lives down the road who'll employ a few kids to do the landscaping... (I jest but also I've actually seen that happen.)