Unions, in general, aren't monolithic. How the average trade union member may feel about contractors within their field would likely depend on the industry they work in.

Further, these groups aren't mutually exclusive in some cases. Many contract electricians are unionized, for example.

Make sure you understand the difference between a contractor and an employee.

Often people who should be employees are classified as contractors.

In this case, a union would advocate that contractors are really misclassified employees.

No, contractor and freelancer unions exist.