A proposed amendment to the Arizona state constitution to limit marriage to opposite-sex couples is facing a fierce battle and opponents of the measure say they are confident it will be defeated.

The survey, by PBS affiliate KAET, has found that 49 percent of those polled support the amendment while 42 percent are opposed.

State Rep. Kyrsten Sinema (D-Phoenix), who is leading the fight against the amendment, said the numbers show support is waning.

Sinema said that supporters of the measure have mounted a major campaign but that the opposition is just now preparing its first big ad buy. TV spots will begin running next week.

In 2006, a similar amendment to ban same-sex marriage and civil unions failed when put to voters. The current amendment proposal does not mention civil unions.

Religious leaders across the state are telling their respective denominations to support the amendment.

Catholic bishops said the amendment is “in alignment with our deeply held moral beliefs