Spain's Justice Minister Mariano Fernandez Bermejo resigned a day after a hunting trip he shared with a prominent judge investigating opposition party members became an issue in regional elections.

The conservative opposition, under pressure from the corruption probe led by Judge Baltasar Garzon, had said the expedition made by the judge and the minister to shoot deer in Andalusia showed the government was too close to the judicial system.

"I can't tolerate the use being made of this against those of us who are working for the ideals of the Socialist government," Mr Bermejo, who also faced an unprecedented strike by judges last week, told a news conference.

It was the first resignation of a minister under Prime Minister José Luis Rodriguez Zapatero, who has led the government since 2004, and came as the Socialists face elections in the Basque Country and Galicia on Sunday.

Opposition Popular Party leader Mariano Rajoy had repeatedly called on Mr Bermejo to resign. The PP says Judge Garzon's investigation, which has implicated party members involved in local politics, is designed to damage its electoral chances.

"By resigning, Bermejo admits his political responsibility and puts an end to an appalling period as minister," said the PP's justice spokesman, Federico Trillo. But it doesn't clear up the worst thing of all: Bermejo's connivance with Garzon," Mr Trillo told reporters.

Mr Bermejo's discomfort has received much media coverage, and conservative newspapers have printed photographs of the bearded minister posing with dead deer.

Up until now, polls have indicated the Socialists could boost their number of seats in both the regional votes.

In contrast with other European governments during the financial crisis, Spain's Socialists have maintained or even boosted their popularity despite a recession and a near doubling in unemployment since 2007 to 14 per cent.