The first time you write the name of an organisation, it must be written in full, with the abbreviation afterwards in brackets.
Example: Nursing and Midwifery Council (NMC)
Thereafter, you can use the abbreviation without writing the full name first, this includes citations.
Example:The professional code of ethics for midwives clearly states… (NMC, 2018).
If you have not already introduced the abbreviation in the main body of your work, or cited the organisation, then the citation for the first mention of the organisation would be formatted as follows:
Example: The professional code of ethics for midwives clearly states… (Nursing and Midwifery Council (NMC), 2018).
The reference in the reference list needs to match your citations.
Example: NMC (2018) The Code. NMC [online]. Available from: https://www.nmc.org.uk/standards/code/ [Accessed 5 March 2019].