Nicola Sturgeon used her column in the Daily Record newspaper on Monday to heavily criticise Ms Davidson’s defence of the tax credits measure.
The rule requires rape victims claiming tax credits for a third or subsequent child to prove they became pregnant as a result of an attack or while in a coercive relationship in order to qualify.
The policy has sparked a political row in Scotland.
It led to a protest in Glasgow last week, attended by around 300 people.
Ms Davidson has said she supports the exemptions the UK Government has put in place on restrictions to child tax credits, saying she wants to see ministers ‘’implement them in the most compassionate way possible’’.
“The last few days have exposed the full horror of the rape clause, the wider issues around the cap on child tax credits and the complicity of Scottish Tories in the utterly immoral policies of their Westminster colleagues,” she wrote.
“Having repeatedly failed to speak out against this disgusting policy, Ruth Davidson then tried to hide behind her official spokesperson.
“And then, last week, she came out in open support of the rape clause. She also made the suggestion that the Scottish Parliament should simply step in and pay for these benefits instead.
“The solution is for the Tories to scrap the rape clause and the two-child policy - not just in Scotland but across the whole of the UK.”
The Scottish Conservatives have been approached for a comment.