The CDU would be excluded from the event this year because of certain politicians' "undignified" and "indecent" remarks arguing against marriage and equality for gay couples in recent debates, said parade organizer Robert Kastl in a statement on Tuesday.
The chancellor's conservative party reject same-sex marriage and have been dragging its feet over implementing a demand by Germany's highest Constitutional Court to grant gay and lesbian couples the same tax breaks and adoption rights as straight married couples.
On Saturday June 22, hundreds of thousands of people are expected to attend the Christopher Street Day parade in Berlin, along with smaller events across Germany and Switzerland. Last year, organizers said 700,000 people attended in the German capital alone.
And this year's parade, set to take place just three months ahead of national elections, could get highly political, said Kastl in his statement, released on the day politicians voted to legalize gay marriage in neighbouring France.
In protest against the CDU's stance, this year's parade will be motto: "No more empty speeches! Demonstrate! Vote! Change!"
Same-sex marriage supporters have celebrated several successes this year, with not only France, but also Uruguay and New Zealand becoming the latest to join 14 countries worldwide in which gay and lesbian couples can marry.
British MPs voted in February for a bill allowing same-sex marriage in the UK, even though the Conservative Party is in power.
In Germany at the end of March, the Bundesrat upper house of parliament passed an initiative to allow gays to marry, which has yet to be put before the Bundestag lower house of parliament.
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While the CDU will be denied its usual big float, organizers welcomed members of the LSU gay and lesbian party sub-group and all those who clearly reject their party's position to participate.
The Christopher Street Day parades commemorate the Stonewall uprising of June 28, 1969, when police harassment at a New York gay bar sparked five days of rioting that launched the US gay rights movement.