Stung by complaints about political ads that have been appearing on the Web sites of its AdSense publishing partners, Google is advising publishers how to block its ads.

"When we notice a spike in readers who are interested in a specific topic, we like to address it as soon as we can," said Arlene Lee of Google AdSense support in a blog post on Monday. "There's been some interest in filtering ads from publisher pages, so here's a quick refresher on the filtering tools we offer."

Google offers a Competitive Ad Filter, which allows AdSense publishers to restrict contextually-targeted and placement-targeted ads that appear on their Web sites by URL. Its Ad Review Center provides broad ad control by allowing publishers to review specific ad groups and advertisers and to block ads by type.

The spike in AdSense publishers asking about ad blocking is the result of the expensive, divisive battle over California's Proposition 8, which aims to amend the state's constitution to disallow gay marriage.

In September, Google came out against Proposition 8. "[W]hile there are many objections to this proposition -- further government encroachment on personal lives, ambiguously written text -- it is the chilling and discriminatory effect of the proposition on many of our employees that brings Google to publicly oppose Proposition 8," said Google co-founder Sergey Brin in a blog post. "While we respect the strongly-held beliefs that people have on both sides of this argument, we see this fundamentally as an issue of equality."

But the company nonetheless has accepted online ads both for and against Proposition 8. "Google allows ads that advocate for a particular political position regardless of the views that they represent," a Google spokesperson explained in an e-mailed statement. "We currently allow ads advocating both for and against Proposition 8."

But opponents of Proposition 8 argue that in doing so, Google is violating its AdSense content policy. Google says that sites displaying Google ads may not include, among other things, violent content, racial intolerance, or advocacy against any individual, group, or organization.