There are two broad categories of strikers.
"Economic strikers" are those employees who strike in order to obtain some economic concession from the employer such as higher wages, shorter hours, or improved working conditions. These strikers retain status as employees. The employer cannot discharge these strikers, but is able to replace them. If an employer has hired legitimate permanent replacements to fill the positions that the economic striker previously held at the time when the striker applies unconditionally to return to work, the striker is not entitled to be reinstated at that time. However, if the striker has not then obtained regular employment that is substantially equivalent to their previous position, the striker is entitled to be recalled to positions for which the striker is qualified once openings in such jobs occur. However, either the striker, or a bargaining representative acting on behalf of the striker, must have made an unconditional request for the reinstatement of the striker.
The second broad category of strikers is "unfair labor practice strikers" which are employees that strike in protest of their employer's unfair labor practice. The company may not discharge nor permanently replace these strikers. Once the strike ends, "unfair labor practice strikers", barring serious misconduct (such as engaging in a violent strike or a "wildcat" strike), are entitled to return to their positions with the employers regardless of whether or not the employer must first discharge the employees hired to replace the striker during the strike. Upon a finding by the National Labor Relations Board that an employer unlawfully denied reinstatement of either economic strikers or unfair labor practice strikers who have unconditionally requested reinstatement, the Board may grant such strikers an award of back-pay starting from the time reinstatement should have taken place. An economic striker whose employer discharges the striker before hiring a replacement may be converted into an unfair labor practice striker.