It is, generally speaking, good practice for an Employer to consult with Employees before introducing changes especially where they are detrimental to the Employees.  In a situation where the Employees may not agree and the Employer is seeking to impose the change, failure to consult could lead to a successful constructive/unfair dismissal claim.  Consultation should be with individuals.  Where there are 20 or more Employees affected there may be a requirement to consult representatives.  There is also a requirement to consult with representatives where contract change follows certain business transfers or changes in contractor.