| Abbreviation | Definition |
|---|---|
| ATAP | Aircraft Technologists Association of Pakistan |
| ATCU | Alabama Teachers Credit Union |
| ATCU | Associated Train Crew Union |
| ATFCU | Alcoa Tenn Federal Credit Union |
| ATFCU | Alcoa Tennessee Federal Credit Union |
| ATLU | Antigua Trades and Labour Union |
| ATLU | Assam Tea Labour Union |
| ATMA | American Textile Machinery Association |
| ATS&GWTU | All Trinidad Sugar and General Workers' Trade Union |
| ATTU | Asian Table Tennis Union |
| ATU | African Telecommunications Union |
| ATU | Amalgamate Transit Union |
| ATU | Amalgamated Transit Union |
| ATUC | Aden Trade Union Congress |
| ATUC | African Trade Union Congress |
| ATUC | Azerbaijan Trade Unions Confederation |
| ATWU | Amalgamated Textile Workers' Union |
| ATWU | Australian Textile Workers' Union |
| ATWU | Australian Timber Workers Union |
| AU | American Union |