Prime Minister Malcolm Turnbull has branded the 2013 Senate election result "an embarrassment" and the preference deals that delivered power to the micro-parties a "disgrace" as upper house crossbenchers came together to plot revenge for the Coalition's voting reforms.

In his strongest comments yet on the issue, Mr Turnbull told the NSW Liberal Party faithful on Saturday he was seeking to "restore democracy" with his bill to introduce optional preferential voting, which would purge Parliament of the micro-parties. The bill is expected to pass this month with Greens support.

Prime Minister Malcolm Turnbull kept the plebiscite policy adopted by Tony Abbott. Credit:Andrew Meares

"The 2013 Senate election was really an embarrassment for Australian democracy," he said at the Liberal State Council meeting on the Central Coast.

"People elected through back-room preference whispering deals, elected on a tiny percentage of votes, was a disgrace."