McDonald's Japan said it may have sold salads and other items past their expiration dates at as many as four of its Tokyo outlets after employees switched production labels.

Shares of McDonald's Holdings Co, which is more than half owned by the US fast-food giant McDonald's Corp, fell 2.4 percent on the news.

Employees relabelled some unsold salads so they could be sold on the following day, in violation of the company's rule that salads are sold within 12 hours of preparation. The company said it had yet to determine whether or not the salads were past their expiration dates when sold. Some employees also admitted to using yoghurt and milkshake mix that were past their due dates, although McDonald's said it was still investigating.

"I think this is terrible," McDonald's Japan chief executive Eikoh Harada told a news conference. "However, I don't think this was a regular occurrence." Harada said the employees had been instructed by senior staff to use the items in order to save expenses.

The company said it had ended its franchise agreement with the four restaurants, all of which were owned by the same franchisee. The outlets will now be operated directly by McDonald's.