Beat the Press - Workers cannot be compelled to join a union anywhere in the United States. They currently can be required to pay a representation fee in a workplace represented by a union. Under the law, a union is obligated to represent all the workers in a bargaining unit, whether or not they join the union. This means that all workers will benefit in the same way from the wages and benefits negotiated by the union. Also, the union is obligated to defend a worker in disciplinary matters or other individual issues even if they are not members of the union.
Twenty six states now deny workers the right to negotiate contracts that require all workers to pay for the representation they get from a union. Apparently, some of those associated with Trump also want to prohibit workers from negotiating contracts under which the employer deducts union dues as a service to the union.
This is an issue about freedom of contract, where the government is limiting what sort of contracts unions can sign with an employer. It is not an issue about individual rights. Any worker who doesn't like unions has the option to work at a workplace where employees are not represented by a union. Just as an employer can impose conditions on workers (for example, wearing a silly uniform or requiring workers to address customers in a particular way), current law allows contracts under which workers set conditions on employment for their co-workers. Apparently people associated with Trump want to take away this right.