Without union protection, workers do not have a right to be re-hired after a layoff. They do not have a right to be laid off in order of seniority (so that the newest workers are laid off first).
Union workers have many more protections. Read your union contract and talk to a shop steward or union leader.
Workers do have legal protection when they are not called back because of retaliation or discrimination. For example, it is illegal to refuse to re-hire workers because they did something which is protected by law (like filing a complaint with a government agency or organizing a union) or to discriminate because of age, race, sex, or national origin.
If a large group of workers is laid off, they may be covered by the Worker Adjustment and Retraining Notification (WARN) law. The company has to give workers advance notice and may have to pay severance. WARN covers big layoffs at a company because of restructuring, contracting out, or closing a department, as well as factories that are closing.
Bankrupt Companies Call your state Department of Labor to find out how to get your name (and your coworkers) listed as a creditor and ask if you can file a preferred wage claim.