Yep. While you do have a right to strike and cannot be fired for striking, you can be replaced. In addition, if you engage in an economic strike, you would generally become an "economic striker."
As an economic striker, your employer is legally allowed to hire a permanent replacement to fill your job. As/if you and/or the union call off the strike, you are not entitled to your job back until a vacancy occurs. Instead, you would be placed on a preferential rehire list and may return to work only when an opening occurs.
The Right to Strike | NLRB
"Economic strikers defined. If the object of a strike is to obtain from the employer some economic concession such as higher wages, shorter hours, or better working conditions, the striking employees are called economic strikers. They retain their status as employees and cannot be discharged, but they can be replaced by their employer. If the employer has hired bona fide permanent replacements who are filling the jobs of the economic strikers when the strikers apply unconditionally to go back to work, the strikers are not entitled to reinstatement at that time. However, if the strikers do not obtain regular and substantially equivalent employment, they are entitled to be recalled to jobs for which they are qualified when openings in such jobs occur if they, or their bargaining representative, have made an unconditional request for their reinstatement."
As an economic striker, your employer is legally allowed to hire a permanent replacement to fill your job. As/if you and/or the union call off the strike, you are not entitled to your job back until a vacancy occurs. Instead, you would be placed on a preferential rehire list and may return to work only when an opening occurs.
The Right to Strike | NLRB
"Economic strikers defined. If the object of a strike is to obtain from the employer some economic concession such as higher wages, shorter hours, or better working conditions, the striking employees are called economic strikers. They retain their status as employees and cannot be discharged, but they can be replaced by their employer. If the employer has hired bona fide permanent replacements who are filling the jobs of the economic strikers when the strikers apply unconditionally to go back to work, the strikers are not entitled to reinstatement at that time. However, if the strikers do not obtain regular and substantially equivalent employment, they are entitled to be recalled to jobs for which they are qualified when openings in such jobs occur if they, or their bargaining representative, have made an unconditional request for their reinstatement."