A more thorough explanation:

Secondary boycotts occur when a group boycotts a company that does business with another company that is involved in a dispute. This usually happens in labor disputes when a labor organization tries to pressure an employer by getting their suppliers or buyers to stop doing business with them. However, this is not allowed under Section 8 of the National Labor Relations Act because it can cause instability in the economy and harm uninvolved parties.

A labor union is in a dispute with a company over wages and working conditions. The union decides to boycott the company by encouraging people not to buy their products. However, the company continues to do business with a supplier who provides them with materials. In order to increase pressure on the company, the union decides to boycott the supplier as well, hoping that this will force the company to negotiate with them. This is an example of a secondary boycott.

Another example could be a group boycotting a store that sells products made by a company they are in dispute with, even though the store itself is not involved in the dispute.

These examples illustrate how a secondary boycott involves targeting a company's business partners or suppliers in order to indirectly pressure the company to resolve a dispute. However, this is not allowed under Section 8 of the National Labor Relations Act because it can harm innocent parties and cause economic instability.