Question: the federal law which made closed shops and preferential shops illegal was the
[{'answer': 'Taft -- Hartley Act'}, {'provenance': [{'wikipedia_id': '553722', 'title': 'Closed shop', 'start_paragraph_id': 5, 'start_character': 0, 'end_paragraph_id': 5, 'end_character': 842, 'bleu_score': 0.946170110139511, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 4125759523871144913}, 'section': 'Section::::Legal status.:United States.\n'}]}]