The prime minister said it was a "complete misconception" to suggest the MPs were opposing the Queen's Speech as a whole by tabling the amendment, and repeated his position that he was "relaxed" about how backbenchers voted.
But last June the Supreme Court ruled that the CDA violated adults' First Amendment rights, leaving the whole issue of children and the Internet in something of a legal vacuum.
The two senators want to see the establishment of a bipartisan commission that would draw up a programme of budget reform to be submitted to Congress for a straight up or down vote, with no possibility of amendment, since amendments would surely cause the whole thing to unravel.