Rafael Nadal has a banana during the French Open. Campaign groups say the flow of bananas from Colombia will dry up within a fortnight of the start of a strike. Photograph: Jason Cairnduff/Action Images

Rafael Nadal has a banana during his quarter-final match in the French OpenBreakfast lovers and tennis players look away now. The UK faces a shortage of bananas, after 18,000 Colombian workers voted to strike over pay.

The campaign group Banana Link is predicting that 288 farms across Urabá in western Colombia will be “paralysed” in the next two weeks if the strike goes ahead. “The flow of well over a million boxes per week, mostly to northern Europe, will dry up within a fortnight of the start of the strike,” it has warned.

Bananas are the UK’s most popular fruit, and more than one in five imported into this country are grown in Colombia.

Campaign groups say bananas are sold too cheaply, although pay and working conditions in Colombia are seen as above average for the tropical fruit industry.

According to the Fairtrade Foundation, a kilo of bananas cost consumers an average of £1.08 in November 1997, but today sells for just 68p. Tesco and Asda were both selling bananas for 68p a kilo on Friday.

Banana Link said the crisis showed that “bananas on the cheap … are simply not sustainable”.

Tropical fruit company Fyffes, a major importer of bananas into Europe, said it was monitoring the situation. “Contingency plans are being put in place to minimize any impact on customers should the strike go ahead,” a spokeswoman told the Grocer.

According to the magazine, Colombian workers are seeking a two-year pay deal that gives them an 8% pay rise in the first year, followed by a 5% rise in the second.

“We recognise that the industry is facing a serious crisis, but it is not for workers to pay the price of a crisis that only the companies and the government can resolve,” the president of Sintrainagro, the Colombian agricultural workers’ union, has said.