Yes. These are set out in General Specifications and in the Basic User Guide. You must comply with them or the bar code may not scan reliably. (You will find the Basic User Guide a more concise and user-friendly source than General Specifications which are very comprehensive and more suited to the advanced technical user)
The GS1 General Specifications document is updated regularly. Go to the GS1 website for the latest version <here>.
Or download the Basic User Guide attached: