Which institution provides technical assistance to labor organizations and employer organizations?

The correct choice is the Institute of Labor and Manpower Studies because this institution is specifically designed to conduct research and provide technical assistance tailored to the needs of labor organizations and employer organizations. Its primary focus is on labor relations, workforce development, and policy-making, aiming to improve the understanding and management of labor-related issues.

Both the Department of Labor and the National Labor Relations Board serve broader regulatory roles and are more focused on enforcing labor laws and regulations rather than providing direct technical assistance. The Department of Labor oversees the welfare of wage earners and job seekers, while the National Labor Relations Board is responsible for protecting employees' rights to organize and bargain collectively. The Workers' Union Bureau may be involved in advocacy or support for unions but does not specifically focus on providing the kind of technical assistance that labor and employer organizations require in their operations and negotiations.