Instead these outlets are selling Finnish milk under the Swedish-owned brand Arla Ingman. The SOK Group, which owns the S grocery stores, says the decision is based on price, availability and logistics -- and stresses that the milk on sale will remain 100 percent Finnish. The S group has been offering Arla milk for a year now.

On Friday the daily Helsingin Sanomat reported that SOK subsidiary HOK-Elanto has 143 shops in the capital region, which sold around 50 million litres of milk products last year. Half of these were manufactured by Valio.

Vanhanen argues that consumers should have the right to choose which brand to buy. He writes in his blog that he was shocked when he could not find basic Valio milk in the dairy department of the grocery store where he has shopped for 25 years. As a result, he says he has switched to a rival supermarket.

Vanhanen is chair of the Centre Party, formerly the Agrarian Party, which has strong roots in Finland's agricultural community. A 54-year-old divorcee with two teenaged children, he is from Nurmijärvi in Uusimaa province.