attempt to suppress government workers' right to strike, including for teachers, police and firefighters, without adequate alternatives to set fair wages. Workers have the right to take protected concerted activity. But NLRB v Insurance Agents' International Union held that although employees refusing to perform part of their jobs in a "partial strike" was not a failure to act in good faith, they could be potentially be discharged: perversely, this encourages workers to conduct an all-out strike instead. Second, since 1947 the law made it an "unfair labor practice" for employees to take collective action that is not a "primary strike or primary picketing" against the contractual employer. This prohibition on solidarity action includes a ban on employees of a subsidiary corporation striking in concert with employees of a parent corporation, employees striking with employees of competitors, against outsourced businesses, or against suppliers. However the same standards are not applied to employers: in NLRB v Truck Drivers Local 449, the Supreme Court held that a group of seven employers were entitled to lock out workers of a union at once, in response to a strike at just one of the employers by the union. This said, employees may peacefully persuade customers to boycott any employer or related employer, for instance by giving out handbills. Third, a union is bound to act in good faith if it has negotiated a collective agreement, unless an employer commits an unfair labor practice. The union must also give 60 days warning before undertaking any strike while a collective agreement is in force. An employer must also act in good faith, and an allegation of a violation must be based on "substantial evidence": declining to reply to the National Labor Relations Board's attempts to mediate was held to be insubstantial. The fourth constraint, and most significant, on the right to strike is the lack of protection from unjust discharge. Other countries protect employees from any detriment or discharge for strike action, but the Supreme Court held in NLRB v Mackay Radio & Telegraph Co that employees on strike could be replaced by strikebreakers, and it was not an unfair labor practice for the employer to refuse to discharge the strikebreakers after the dispute was over. This decision is widely condemned as a violation of international law. However the Supreme Court further held in NLRB v Fansteel Metallurgical Corporation that the Labor Board cannot order an employer