Yellow-dog contracts are employment contracts that require workers to refrain from joining a union. They are also known as anti-union contracts, ironclad oaths, and anti-organizing agreements. These contracts are considered controversial as they are seen as a violation of workers' rights to join unions and collectively bargain for better wages and working conditions. Other synonyms for yellow-dog contracts include union-free contracts, no-union contracts, closed-shop agreements, and union-suppression agreements. Some jurisdictions have outlawed yellow-dog contracts as they are seen as an unfair labor practice. Employers who use yellow-dog contracts often face criticism and opposition from workers' rights groups and unions.