Which of the following is NOT a type of fund started to help union contractors?

The distinction lies in the purpose of each type of fund in relation to supporting union contractors. Education funds, healthcare funds, and promotion funds all directly aim to enhance the welfare and operational capacity of union contractors.

Education funds are particularly focused on providing training and development opportunities for workers, which helps to improve their skills and employability. Healthcare funds are designed to ensure that union members have access to essential health services, improving their overall well-being and job security. Promotion funds are utilized to market and advocate for the union's services, effectively helping contractors gain visibility and work opportunities.

In contrast, investment funds are not specifically geared towards the immediate support of union contractors in the same way. While they can certainly play a role in the broader financial health of organizations, they lack the direct connection to promoting contractor health, education, and market presence. Thus, investment funds do not fit within the same framework as the other options listed, making it the correct choice for the question asked.