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The Internal Revenue Service is recalling about 46,000 employees furloughed by the government shutdown to handle tax returns and pay refunds. The employees, nearly 60 percent of its overall workforce, won't be paid for their work during the shutdown.

Meanwhile, at the Food and Drug Administration inspections of food facilities are resuming, again, using unpaid staff, as hundreds of furloughed employees are returning to restart "high risk" food inspections that were halted during the government shutdown.

Unlike other private employees, the unpaid federal workers on the job without pay have long been legally prohibited from striking to protest these conditions.

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On Aug. 3, 1981, after several months of negotiation with the FAA, several thousand air traffic controllers went on strike. In response, then-President Ronald Reagan ordered these federal employees to return to work within 48 hours or risk losing their jobs. Over 11,000 controllers refused, so Reagan fired them and banned them from returning to work at the FAA, ever.

That ban was not an overreach of executive power. Federal law provides that federal employees who participate in a strike against the government are barred indefinitely from government employment, and may even be subject to criminal prosecution.

Although striking against the federal government is a felony, prosecutions have been rare. One court has observed it is the "sworn duty of the Attorney General to enforce these laws…but for reasons not fathomable by this court they have apparently yet to initiate any investigations or enforcement proceedings."

While prohibited from striking, federal employees have statutory collective bargaining rights. The Federal Service Labor-Management Relations Statute ("FSLMRS") recognizes that labor unions and collective bargaining safeguard the public interest and facilitate settlement of disputes involving conditions of employment. The law affirms the rights of federal employees to unionize and to engage in collective bargaining but it also determines what can — and cannot — be bargained.

For example, "permissible" bargaining includes negotiation as to the numbers, types, and grades of employees assigned to a project, or the technology, methods and means or performing work.

On the other hand, the FSLMRS prohibits negotiation over management rights or areas subject to government-wide regulations. Employees' bargaining rights cannot interfere with federal agencies' right to determine the budget, hiring, layoffs, suspensions or reductions in pay. Collective bargaining rights do not extend to regulations that are generally applicable throughout the government.

Federal employees have limited collective bargaining rights. While they may assert theories of involuntary servitude or violations of wage laws, those who are ordered back to work face stiff penalties if they refuse or strike against the government.

Danny Cevallos is an MSNBC legal analyst. Follow @CevallosLaw on Twitter.