Much of federal labor law is codified in title 29 of the U.S. Code. In addition to the proprietary databases listed below, Title 29 is freely available at Cornell's Legal Information Institute and GPO's FDsys.
CRS Report Federal Labor Relations Statutes: An Overview provides a great review of the aims of 3 federal labor statutes governing labor-management relations for private sector and federal employees. It includes cites to some elements of the statutes’ legislative history.
In addition to the below proprietary databases, some recent administrative decisions, orders, information and guidance are freely available at the websites of agencies such as the National Labor Relations Board, the National Mediation Board, the Federal Labor Relations Authority, and the Federal Mediation and Conciliation Service.