The Communication Workers Union (CWU) is to make equality and diversity training a condition of becoming a union representative.
The union is to spend £300,000 on putting its 6,000 reps through a one-day equality and diversity training course to help them understand the culture and beliefs of the staff they represent.
The CWU decided to ensure all its union representatives go through equalities training after experiencing diversity problems at the troubled Royal Mail Group which led to a bullying and harassment culture.
These were highlighted earlier this year when the struggling firm, which is losing more than £1m a day, admitted that racist managers led a black postman to commit suicide.
Billy Hayes, general secretary at the CWU, believes that if union reps have a better understanding of different cultures and beliefs, they can help to defuse potential problems.
"They (union representatives) are a volunteer army so we want to look at training for them. Royal Mail Group is a labour-intensive industry so there is always going to be tension and conflict, but it is how you manage it and get on to a similar agenda that we are looking to address," he said.
"It is important that union reps know how important it is to have a good, safe workplace. Royal Mail Group is already broadly reflective of the community and diversity awareness becomes more important with more women and ethnic minorities entering the workforce."
CWU has 3,000 union reps in the Royal Mail Group.