Mr Wallace said any move to water down the ALP's platform on marriage at its annual conference in Sydney this week would break faith with this election promise.
"That commitment was made for the life of the Rudd Government and that is what we would expect to be honoured," Mr Wallace said.
"Evangelical and Orthodox Christians in particular have been very tolerant in the removal of discrimination from same-sex couples but do not wish to see the institution of marriage undermined to placate the demands of noisy activists representing around two percent of the population.
"If the Labor platform is amended to allow schemes which mimic marriage Labor risks driving many Christians to the right who would otherwise be drawn to the party because of its emphasis on social justice," Mr Wallace said.