It is very simple to draft a letter addressing the union secretary or president.
To: The Union Secretary / President
Name of union: [Insert Name]
Dear Sir,
Subject: Intimation of Joint Meeting - Regarding
Ref: Charter of Demands dated [Insert Date] as submitted by your union - Regarding
With reference to the above, please be informed that our unit head has tasked me with organizing a joint meeting with the office bearers of your union at [Insert Time] on [Insert Date]. This meeting aims to facilitate discussions and reach an amicable settlement regarding the demands outlined in the charter of demands referenced above.
Hence, we kindly request the presence of 6 or 7 executive members from your union at the aforementioned meeting, scheduled at the HR Dept conference Hall at [Insert Time] on [Insert Date]. Please note that permission for the union representatives to leave their workstations to attend this meeting will be granted by their respective service departments.
Regards,