The Huffington Post on Friday rebuffed a union boycott call over its practice of using unpaid bloggers, saying most of them are "thrilled to contribute" despite not being paid.

The Newspaper Guild, a union of US media workers with 26,000 members, urged contributors to The Huffington Post earlier this week to stop providing free content to the news and opinion website.

"Just as we would ask writers to stand fast and not cross a physical 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," the guild said. "Working for free does not benefit workers and undermines quality journalism."

The guild urged founder, Arianna Huffington, who sold The Huffington Post to Web company AOL this month for $315 million, "to demonstrate her commitment to the working class she so ardently champions" by paying bloggers.

Mario Ruiz, a Huffington Post spokesman, said Friday that the site is "squarely behind the Newspaper Guild's mission of ensuring that media professionals receive fair compensation.

"It's why we employ a newsroom of 160 full-time editors and reporters, 17 of whom we've hired since last Monday," Ruiz said in a statement.

"However, we make a distinction between our newsroom staffers and our group bloggers -- most of whom are not professional writers but come from all walks of life," he said.

"The vast majority of our bloggers are thrilled to contribute," Ruiz continued. "And we're thrilled to have them."

"Bottom line: nearly all of our bloggers are happy with the arrangement, and happy to access the platform and the huge audience it brings, without having to build, pay for, edit, moderate or maintain that platform," Ruiz said.

"Indeed, we are inundated with requests from people who want to blog," he said. "The proof is in the pudding: people are looking to join the party, not go home early."

The Huffington Post has attracted a strong following -- nearly 25 million unique visitors a month -- to its lively mix of news, entertainment, opinion and blogs submitted by academics, entertainment figures and politicians.