VIENNA (Reuters) - Austria's Protestant church criticized the far-right candidate for president on Monday for using the phrase "so help me God" on his campaign posters, saying his party's anti-immigrant stance ran against Christian principles.

Norbert Hofer, the anti-immigrant Freedom Party's (FPO)presidential hopeful, uses the line in the hope it will help persuade voters to make him the European Union's first far-right head of state in a run-off election on Dec. 4.

The result of a previous run-off in May, which the 45-year-old eurosceptic narrowly lost to former Green Party leader Alexander Van der Bellen, 72, was annulled due to irregularities in counting postal ballots.

Hofer is a former Catholic turned Protestant who has said he would not swear in a female minister wearing an Islamic headscarf.

"God can not be instrumentalised for one's own intentions or for political purposes," the three branches of the Protestant churches in the Alpine republic said in a joint statement.

Austria is a traditionally Christian country where two-thirds of the 8.7 million population are professed Catholics and about four percent are Protestant.

While a spokesman for the Austrian Bishops' Conference - the highest body of the Catholic church - said the church would not comment on Hofer's campaign, the Protestant church said Hofer had misused Christianity for narrow political ends.

"We do not get involved in party politics, but if Christian principles are violated we have to take a...stand," said Thomas Hennefeld, superintendent of the Protestant Reformed Church.

Hofer's direct invocation of God for political purposes was the first of its kind in Austria for 10-15 years and was inappropriate given the FPO's politics, Hennefeld said.

"We stand for a Biblical understanding of God, a universal God who is there for the weak, the strangers, the refugees - the opposite of what the FPO stands for."

Austria has taken in over 115,000 migrants from the Middle East, Africa and Asia since last year. After initially welcoming the refugees, more and more Austrians fear it will be difficult to integrate the newcomers and have become receptive to the FPO's message that mass immigration threatens security and jobs.

FPO head Heinz-Christian Strache dismissed the Protestant churches' criticism, arguing that "so help me God" was also part of the presidential swearing-in vow.

"I simply cannot understand how it is necessary to justify oneself when it comes to one's core values," Strache said.

(Reporting by Kirsti Knolle; editing by Mark Heinrich)