A conservative watchdog group is asking the Office of Congressional Ethics on Thursday to review whether 14 Democratic lawmakers and one Republican inappropriately used their office to try to coerce a Las Vegas casino mogul into allowing his employees to unionize. In May, Wisconsin Rep. Mark Pocan and 13 other Democrats wrote a letter to Frank Fertitta III, the CEO of the Las Vegas-based casino management company Red Rock Resorts Inc., urging him to “respect the rights of employees” at the company “to form a union and collectively bargain.” Republican Rep. Brian Fitzpatrick of Pennsylvania sent Fertitta a similar letter...