In a letter to her government colleague seen by AFP she called on him to abandon his insistance on waiting for a decision on the issue by Germany's top court.
Both Leutheusser-Schnarrenberger and Economy Minister and Vice-Chancellor
Philipp Rösler are in favour of changes to the law to allow registered partnerships of same-sex couples, introduced in Germany in 2001, the same tax benefits as married heterosexual ones.
Both ministers are members of the pro-business Free Democrats, a junior partner in Chancellor Angela Merkel's fractious centre-right coalition.
On Wednesday Schäuble, a Christian Democrat like Merkel, directly contradicted his colleagues in cabinet, with his spokeswoman noting that marriage enjoyed special protection under Germany's Basic Law.
She said Schäuble, unlike other members of the government, currently saw no need for a speedy tax reform and would await the court decision due by next year.
Deputy government spokesman Georg Streiter also highlighted to reporters the need to wait for the Federal Constitutional Court's ruling "in order to then get it right."
On Tuesday, Family Minister Kristina Schröder had welcomed in a German newspaper a push for a swift revision to the law by 13 deputies from Merkel's conservative Christian Democratic Union (CDU), sparking a debate in Berlin.
Couples in lesbian and gay partnerships assumed a long-term responsibility and thus lived according to "conservative values", she told the centre-left Süddeutsche Zeitung paper.
Both Schröder and Schäuble are part of Merkel's CDU, whose Bavarian sister party, the Christian Social Union, also a coalition partner, strongly opposes the move.
According to estimates, state coffers would reap about €30 million less if formally registered gay couples could also enjoy certain tax benefits applied to married ones.
According to an opinion poll to be published Monday in the weekly Focus, 80
percent of Germans back the move, with only 17 percent against.
Some 23,000 same-sex partnerships are currently registered in Germany, according to federal figures cited by the Süddeutsche Zeitung.