Like a playboy losing his touch, Google (Nasdaq: GOOG) is getting rejected a lot lately.

Google's latest Dear Sergey letter comes from TripAdvisor. According to a Dec. 8 story by Tnooz.com's Kevin May, the popular travel reviews website is quietly blocking its user ratings from populating Google Places, a popular component of Google's mapping site.

If you're looking for an explanation for TripAdvisor shunning the potential of reaching out to Google's many visitors, it helps to examine its family tree. TripAdvisor's parent is Expedia (Nasdaq: EXPE), one of the many online travel portals concerned with Google's pending purchase of Web-based booking specialist ITA Software.

If Google is successful in acquiring ITA, many portals will begin sizing up the world's leading search engine as a competitor. Orbitz Worldwide (NYSE: OWW), Kayak, Microsoft's (Nasdaq: MSFT) Bing, and TripAdvisor rely on ITA for travel information. Other companies -- including priceline.com (Nasdaq: PCLN) and travel deals publisher Travelzoo (Nasdaq: TZOO) -- would feel the sting if Google begins playing a bigger part in reaching out to Web-savvy travel seekers.

In other words, TripAdvisor is no longer interested in sleeping with the enemy.

Google Places doesn't need TripAdvisor, but it obviously helps it beef up its listings until Google cooks up a home-grown solution or acquires Yelp. The bigger concern here is that this is the beginning of the backlash against Google by the travel portals that have historically relied on Google for traffic and leads.

This is a small gesture, but it speaks volumes.

What's your favorite online travel play? Share your thoughts in the comment box below.

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