Democrats, including U.S. President Barack Obama, have generally supported new rules that would prohibit broadband providers from selectively blocking or slowing Web content, but the group of 72 members of the House of Representatives sent a letter Thursday to FCC Chairman Julius Genachowski, saying they're concerned that new regulations would slow down investment in broadband networks. Many of the 72 Democrats are members of the "Blue Dogs," a conservative wing of the party, or of the Congressional Black Caucus.

Although the Congressional Black Caucus isn't traditionally against government regulation, some members are concerned that many African-Americans and other ethnic minorities lack access to broadband networks. Among the House Democrats signing the letter were Elijah Cummings of Maryland, Charlie Gonzalez of Texas and Loretta Sanchez of California.

The FCC on Thursday is scheduled to vote on a notice of proposed rule-making, the first step toward approving formal net neutrality rules. The FCC has had informal open Internet principles since 2005, but cable provider Comcast, in a lawsuit, has challenged the agency's authority to enforce the principles.

The 72 House Democrats join 18 Senate Republicans, a coalition of minority groups, the Communications Workers of America and a coalition of telecom-related companies, including Cisco Systems, Ericsson and Motorola, in raising concerns about new net neutrality rules in recent days.

The FCC should "carefully consider the full range of consequences that government action may have on network investment," the Democratic letter said. "In light of the growth and innovation in new applications that the current [regulatory] regime has enabled, as compared to the limited evidence demonstrating any tangible harm, we would urge you to avoid tentative conclusions which favor government regulation."