HR should be involved at an early stage to ensure the merged entity will not encounter issues down the line relating to motivational issues such as pay scales and promotion opportunities.
Having HR representatives from both companies sit together and identify areas of concern early can help build towards an amicable solution which would not derail PMI efforts. Clear communication around agreed changes can be sent to all employees, and an element of “give and take” can help build goodwill to make target company employees feel that a new regime is not simply being imposed on them.
Cultural fit surrounding HR policies (from dress code to promotions, job title to holiday entitlement), if not handled correctly, can lead to a sense of “them versus us” which can be difficult to reverse.