Question: Local No. 580 of the Teamsters Union was certified by the NLRB as the exclusive bargaining representative for the employees of Adams Potato Chip Co. At subsequent negotiations for a collective agreement covering the employees, the union negotiators indicated that they would accept the company's proposal if the company agreed to change its offer of three weeks' vacation for workers with at least fifteen years of service to three weeks' vacation after ten years of service. The company's lead negotiator agreed to the change and the parties held that the negotiations were completed. The company president later refused to sign the written agreement, claiming that the company negotiator lacked authority to agree to the change in vacation policy. Has the company violated Section 8(a)(5)? Explain.