For years, William Zammer Jr. has relied on 100 seasonal foreign employees to turn down beds, boil lobsters and serve cocktails at the restaurants, golf course and inn he owns on Cape Cod and in nearby Plymouth. This summer, however, the foreign workers will not be returning, and Mr. Zammer, like other seasonal employers across the nation, is scrambling to find replacements. “It’s a major crisis,†he said. “We’re very short on work force. We’ll be looking at opening a little later, closing a little earlier, looking at how we do our menus.†Mr. Zammer is caught up in a...