Opponents of same-sex marriage began airing television ads in Maryland with a spot Monday featuring softly lit images of traditional families and children.

“Marriage, the union of a man and a woman, has served society well for thousands of years,” says the ad sponsored by the Maryland Marriage Alliance. “Marriage is more than what adults want for themselves. It’s also about the next generation.”

The ad marks a new phase of the campaign over next month’s ballot measure on whether to uphold the state’s law that would allow gay and lesbian couples to wed starting in January.

Marylanders for Marriage Equality, the lead group seeking to uphold the law, has reserved air time on television starting Wednesday.

Groups on both sides of Question 6 have spent months mobilizing supporters and raising money to pay for the ads that will dominate the final month of the campaign.

The opponents’ ad also argues that “children do best when raised by their married mom and dad.”

“Everyone is entitled to love and respect, but no one is entitled to redefine marriage,” the ad says.