Federal labor officials said Tuesday they don’t expect to decide before Thursday on whether to seek an injunction on behalf of Wal-Mart Stores Inc. to stop a union-backed group from encouraging worker walk-outs that are expected to culminate Friday. That’s the traditional start of the holiday shopping season. The world’s largest retailer, based in Bentonville, Ark., on Friday filed an unfair labor practice charge with the National Labor Relations Board against the United Food and Commercial Workers International Union. It said the demonstrations organized by union-backed OUR Walmart threaten to disrupt its business and intimidate customers and other store workers....