Conservative senators are warding off a renewed push for a free vote on same-sex marriage for Liberal MPs, warning it would lead to chaos and fail anyway in the party room.

But prominent Liberal MP Alex Hawke, who does not support same-sex marriage, is calling for a conscience vote, saying a showdown is the "only way" to resolve the issue.

Assistant Minister to the Treasurer Alex Hawke. Credit:Andrew Meares

Liberal MPs will need to make a decision on same-sex marriage in the new year, with Liberal Democratic Party senator David Leyonhjelm introducing his marriage equality bill to the Senate on Wednesday evening.

Prime Minister Tony Abbott - who is a strong opponent of same-sex marriage - has repeatedly said that the issue of a free vote on the matter would be a matter for the post-2013 election Liberal Party room.