Does anyone have the option of joining or not joining the union?

It depends on what region you are in.

Some States and Provinces follow the Rand Formula which essentially means: Since everyone receive all perks at working at a union worksite (higher wages, benefits, vacations) everyone must be a member of the union.

If you live in any of these states: Alabama, Arizona, Arkansas, Florida, Georgia, Idaho, Iowa, Kansas, Louisiana, Mississippi, Nebraska, Nevada, North Carolina, North Dakota, Oklahoma, South Carolina, South Dakota, Tennessee, Texas, Utah, Virginia or Wyoming you do not have to be a union member to receive what the union negotiates.