In an open letter Jenna Behrends, a newly elected CDU politician in Berlin, complained that sexism was rife in the party. She felt insulted when a senator called her a "sweet mouse".
Minister for Families Manuela Schwesig said sexist jokes were "unacceptable".
A Green MP also backed Ms Behrends.
Gesine Agena, the Greens' spokesperson on women's issues, said she had also heard "daft language" from male politicians. Sexism "is experienced by many women politicians", she said - though the Greens, unlike the CDU, have a 50-50 quota rule for men and women on their party lists.
Backlash from women
Ms Behrends, a 26-year-old lawyer, said she had experienced "party-wide solidarity" since publishing her "Dear Party" letter on the Edition F website (in German) on 23 September.
However, she lashed out at the CDU's Women's Union for "shutting itself off" and addressing her complaint "internally, at senior level". The union deals with women's issues in the party.
According to Ms Behrends, some of the CDU women members characterised her as "hungry for promotion" and "ambitious to get elected to chair the Women's Union herself".
The union's leader, Sandra Cegla, was quoted as saying Ms Behrends was intimate with Peter Tauber, the CDU's Secretary General and a top aide to Chancellor Angela Merkel.
Quoted by German news website Der Spiegel, Mr Tauber said "I got acquainted with Jenna Behrends and we flirted, but quickly I realised that we would remain friends, no more than that".
Several commentators say Ms Behrends has revived a sexism debate triggered in 2013 by journalist Laura Himmelreich, who complained of harassment by a senior Free Democrat (FDP) politician at the time, Rainer Bruederle.
CDU 'internal' matter
Ms Behrends criticised a party which "enjoys malicious gossip over a few beers". "Women willing to sleep their way to a top local position exist only in your dirty fantasies," she added, in her open letter.
The senator at the centre of Ms Behrends' complaint has been identified as Frank Henkel, a Berlin CDU politician.
He allegedly called Ms Behrends "sweet big mouse" after calling her daughter "a sweet little mouse". And he was said to have inquired about Jenna Behrends' sex life.
The CDU's local mayoral candidate in Berlin-Mitte district, Carsten Spallek, said those involved in the sexism row had had a "frank discussion" on Monday night and agreed that the issue "should henceforth be discussed calmly, in various forums, and only inside the party".
Ms Behrends endorsed that statement, posting it on her Facebook page.
The conservative CDU rules Germany in coalition with the centre-left Social Democrats (SPD).
Women in the CDU
Despite the current row, the CDU has appointed women to some prominent posts, not least Mrs Merkel, who overturned decades of tradition by becoming leader in 2000.
The CDU's Ursula von der Leyen is defence minister, Nadine Schoen is deputy head of the CDU group in parliament and Julia Kloeckner has been tipped as a possible successor to Chancellor Merkel.
Mrs Merkel said recently that Germany had to act more resolutely to tackle sexism.
"It is deplorable that in more than 65 years of the Federal Republic of Germany, the Dax-30 companies haven't managed to get a few more women on to supervisory boards on a voluntary basis," she complained.
"For a long time I opposed statutory quotas. But at times we heard so many hollow promises that it was clear - this isn't working."