Cabinet ministers will ignore Prime Minister Malcolm Turnbull's lead and kill off amendments to the same-sex marriage bill that would have bolstered religious exemptions and enabled civil celebrants to discriminate against gay couples.

Defence Industry Minister Christopher Pyne indicated he would oppose all amendments to senator Dean Smith's bill, deriding the various changes proposed by his Liberal colleagues as unnecessary and superfluous.

Mr Pyne's declaration means there are now enough MPs opposed to the amendments to form a blocking majority of 74 votes, including Labor's 69 MPs, Adam Bandt, Rebekha Sharkie, Andrew Wilkie and Liberal backbencher Warren Entsch.

Fellow Liberal MP Trent Zimmerman took that number to 75, telling Fairfax Media on Tuesday: "I have not seen any amendments that would dissuade me from believing that the bill adopted by the Senate should stand."