It permits strikes in pursuit and enforcement of multi-employer collective agreements. A group of employers who are covered by a multi-employer collective agreement will all face the same labor costs and can easily translate this into uniform product prices. The worst feature of the NLRA copied by the authors of the ERA is mandatory good faith bargaining. New Zealand employers are forced to bargain with unions that represent two or more workers. At least in the U.S. a union must have the support of a majority of an employer's workers before it can force him to bargain.
Mandatory bargaining is bad enough, but the good faith requirement makes things worse.
The NLRA doesn't define good faith either. Employers must watch their language and show proper deference to the union negotiators. It is bad faith for an employers to poll workers to find out what they want. Good faith means only unions can speak for workers whether the workers like it or not. The only effective defense against a charge of bad faith bargaining is a record of concessions to the union.