Union busting is a range of activities undertaken to disrupt or weaken the power of trade unions or their attempts to grow their membership in a workplace.

Union busting tactics can refer to both legal and illegal activities, and can range anywhere from subtle to violent. Labor laws differ greatly from country to country in both level and type of regulations in respect to their protection of unions, their organizing activities, as well as other aspects. These laws can affect topics such as posting notices, organizing on or off employer property, solicitations, card signing, union dues, picketing, work stoppages, striking and strikebreaking, lockouts, termination of employment, permanent replacements, automatic recognition, derecognition, ballot elections, and employer-controlled trade unions.

Article 23 of the Universal Declaration of Human Rights declares that everyone has a right to form or join a trade union. The provision is, however, not legally binding and has, in most jurisdictions, no horizontal effect in the legal relation between employer and employees or unions.

There are many labor relations consultancies worldwide. They specialize in industries such as entertainment (radio, television and motion picture), hospitality (culinary and food service), communications, manufacturing, aerospace, utilities, and healthcare. Although many operate only in the United States, trade union organizing takes place multi-nationally. According to the AFL-CIO, "one of the largest U.S. firms, Labor Relations Institute (LRI), offers a "Guaranteed Winner Package": if the corporation does not "win", it does not pay. Due to the diversification of the US workforce, organizing campaigns increasingly involve immigrant non-English speaking workers. Internationally, compliance with labor laws within developed countries can be vastly different from emerging countries. Both trade union organizers and management must know the law and avoid unfair labor practice (ULP) charges.

Application and adherence to labor laws may differ worldwide, but labor laws continue to expand into new countries such as the Labour Law of the People's Republic of China and the Indian labour law. Trade union organizing often starts with workers who are untrained or unaware of labour law. Due to the changing global and multinational employment environment and labor relations/employment laws, the modern labor movement turns more and more to professional guidance. Internationally, laws differ in how a bargaining unit is defined for workers with job descriptions involving supervision or management. Because the operative word is "law", trade unions and workplaces may retain legal counsel to navigate the complexities of local and/or international labor laws in order to avoid unfair labor practice charges.

Following the repeal of the Combination Laws in 1824, workers were no longer prohibited from forming labor organizations or collective bargaining, although significant restrictions remained. In 1832 the Friendly Society of Agricultural Labourers was formed in Dorset to challenge declining wages. The members of the organization agreed to only work for wages greater than a certain amount. In 1834 a landlord complained, and key members were charged and convicted under laws prohibiting the swearing of secret oaths. The sentence of seven years penal transportation to Australia prompted a movement to defend the members, known as the Tolpuddle Martyrs (referring to the village where the organization originated), who were eventually released in 1836 and 1837.

Presently, UK labor laws are defined within the Employment Relations Act 1999 (ERA) and the Trade Union and Labour Relations (Consolidation) Act 1992, and give individual workers no constitutional right to strike; groups of workers may legally strike only if they conform to numerous conditions. In the UK and EU, trade union opposition may occur during automatic recognition campaigns and ballot elections. Workers in the UK may have union memberships that they retain job to job, potentially resulting in workers for the same employer having different union memberships. When a union is seeking to gain control of the collective bargaining at a place of employment without a ballot, workers with either individual and/or different union memberships working for that same employer may oppose that union.

Consultation is the process by which management and employees (or their representatives) jointly examine and discuss issues of mutual concern. It involves seeking acceptable solutions to problems through an exchange of views and information. Consultation does not remove the right of managers to manage, but it does impose an obligation that the views of employees be sought and considered before decisions are taken. The Advisory, Conciliation and Arbitration Service (ACAS), is the UK government's independent agency for advice and conciliation. Although the Trade Union Congress (TUC) and their member unions oppose the use of consultancies during recognition campaigns, calling it a union busting tactic, ACAS takes a different stance, "Employee communications and consultation are the lifeblood of any business. which "aims to improve organizations and working life through better employment relations".