In April 1975, Martin was chosen as the Liberal Party's assistant whip in the Senate. She was "a linchpin in keeping the Opposition senators in line" during the 1975 constitutional crisis, and retained the position after the Coalition won the 1975 federal election. She resigned as assistant whip in February 1977 after crossing the floor with nine other Liberal senators to oppose a procedural motion to expedite the government's constitutional amendment bills. Martin subsequently led the "No" campaign in Queensland against the simultaneous elections amendment, which was the only one of four not to pass. Her relationship with Prime Minister Malcolm Fraser deteriorated as a result and "destroyed her prospects for promotion while he remained party leader".