Huffington Post has taken a lot of knocks for building its business (which sold to AOL earlier this month for $315 million) partly by using unpaid bloggers. Those knocks became official last week with The Newspaper Guild, a union of media workers in the U.S. with 26,000 members, calling for HuffPo contributors to stop offering free content.

"Just as we would ask writers to stand fast and not cross a picket line, we ask that they honor this electronic picket line," the guild said in a statement. "We feel it is unethical to expect trained and qualified professionals to contribute quality content for nothing. Working for free does not benefit workers and undermines qualify journalism."

The guild went on to call for Huffington Post founder Arianna Huffington to "demonstrate her commitment to the working class she so ardently champions in her writing." (The Guild has created a Facebook page called "Hey Arianna, Can You Spare a Dime?")

In an interview with FoxNews, Huffington Post spokesperson Mario Ruiz says media professionals should get fair compensation (which it does with its 160 full-time editors and staffers) but draws a line between staff and bloggers.

"There’s no commitment; they can post as frequently or infrequently as they would like to," Ruiz said. "The Huffington Post makes no claim of ownership over their posts, and they can cross-post on other sites, including their own."

AOL laid off hundreds of employees since acquiring Huffington Post and putting Arianna Huffington in charge of editorial operations. Ironically, Huff Po seems to be slowly weaning itself away from free blogger content and investing more in full-time staff and name journalists, hiring 17 new journalists over the past week, including John Montorio, former managing editor of The Los Angeles Times and associate editor of The New York Times as culture and entertainment editor and hiring political writer Jon Ward from News Corp.’s The Daily.