The disruption of french fry shipments from the United States is pinching restaurants in Japan, and some have taken special measures to make sure they can meet demand.

The problem is being caused by labor unrest at ports on the U.S. West Coast, where shipments of the fast-food staple originate.

According to the Japan External Trade Organization, the strife began in May as negotiations between dockworkers and shipping lines in Los Angeles, Long Beach and other ports soured over a newly proposed six-year contract. The resulting strikes and other disruptions have slowed the processing of export documents.

To cope, Skylark Co., which runs the Gusto chain of family restaurants, said Thursday it plans to import around 200 tons of fries by air.

McDonald's Co. (Japan) also said on Thursday it has been seeing delays in french fry procurement since mid-November and will try not to let the problem affect it.

Royal Holdings Co., which runs the Royal Host restaurant chain among other others, said it has several months' worth of stock but is carefully assessing the situation as it develops.

If the delay continues, restaurants may have to consider reducing sales or making menu substitutions.

Japan is also struggling with another butter shortage, worrying bakeries as they enter the Christmas season.

Four major butter-makers have agreed to boost output by about 33 percent this month at the request of the farm ministry to meet surging demand for the yuletide season, the ministry said Thursday.

The four companies told the Agriculture, Forestry and Fisheries Ministry the same day that they plan to comply with the request, made last month, before demand peaks for the annual Christmas cake rush.

Last year's sweltering summer and a drop in dairy farmers reduced the production of raw milk, the precursor to butter.