A beverage distributor announced that it was consolidating its operations and closing one of its unionized facilities. The union subsequently entered negotiations with the employer over the effects of the closure on employees. Six drivers heard that there would be a negotiation session held later that morning. They decided to leave work to try to get information about how the consolidation would affect their future employment. The drivers first met at a coffee shop to formulate their questions and then proceeded to the union hall where the negotiating session was being held. When they showed up at the union hall, a union officer advised them to return to work. The drivers persisted and it was agreed that they would have time to introduce themselves to the management representatives. After doing so, the drivers returned to work. All told, they had been gone from work for about three hours. They were subsequently terminated for leaving work without authorization. Did this employer violate the NLRA by terminating these employees for engaging in protected concerted activity?