As thousands of websites and blogs went dark Wednesday to voice their opposition to the Stop Online Piracy Act and the Protect IP Act, some U.S. lawmakers have had a change of heart about the controversial copyright enforcement bills.

Senator Marco Rubio, a Florida Republican, announced Wednesday he was withdrawing as a co-sponsor of PIPA, and Senator John Cornyn, a Texas Republican, called on Congress to take more time to work on the bills.

"Better to get this done right rather than fast and wrong," Cornyn said on his Facebook page. "Stealing content is theft, plain and simple, but concerns about unintended damage to the internet and innovation in the tech sector require a more thoughtful balance, which will take more time."

Rubio also joined several other Republicans in calling for Senate Majority Leader Harry Reid, a Nevada Democrat, to delay a vote on PIPA scheduled for next Tuesday.

"Earlier this year, this bill passed the Senate Judiciary Committee unanimously and without controversy," Rubio said in a Facebook post. "Since then, we've heard legitimate concerns about the impact the bill could have on access to the Internet and about a potentially unreasonable expansion of the federal government's power to impact the Internet. Congress should listen and avoid rushing through a bill that could have many unintended consequences."

Representative Ben Quayle, an Arizona Republican, withdrew his sponsorship of SOPA on Tuesday, and Representative Lee Terry, a Nebraska Republican, said Wednesday he planned to remove his name from the sponsors list.

On Wednesday, Senator Jeff Merkley, an Oregon Democrat, voiced opposition to SOPA and PIPA. "We can't endanger an open Internet," he tweeted. A day earlier, Senator Scott Brown, a Massachusetts Republican, said he opposes PIPA. Neither Brown nor Merkley were co-sponsors of PIPA.

On the other side, giant trade group the U.S. Chamber of Commerce, a strong supporter of PIPA, said it would be watching the upcoming vote and warned that it would include senators' votes in its annual scorecard, which grades lawmakers on a handful of important votes each year.

"The Chamber urges the full Senate to fully debate and pass this important measure," the group said in a letter to senators. "Recent announcements by sponsors of the legislation have made clear that important issues of internet operation, security, and freedom will be addressed by a manager's amendment. The amended legislation is a more narrowly tailored approach designed to target the worst offenders."

A group of musicians and other artists also sent an open letter to Washington Tuesday, saying they were "deeply concerned" about PIPA and SOPA. Many trade groups representing the music and movie industries have been strong supporters of the two bills.

The letter writers, including musicians Trent Reznor, OK Go and MGMT, and author Neil Gaiman, said they are victims of piracy, but they also use a "free and open Internet" to reach their audiences.

"We fear that the broad new enforcement powers provided under SOPA and PIPA could be easily abused against legitimate services like those upon which we depend," the letter said. "These bills would allow entire websites to be blocked without due process."

New York City demonstration against SOPA/PIPA, outside the Manhattan offices of Sens. Charles Schumer and Kirsten Gillibrand, two Democrats who co-sponsored the Senate PIPA bill. (Image: Joab Jackson / IDG News Service)

Grant Gross covers technology and telecom policy in the U.S. government for The IDG News Service. Follow Grant on Twitter at GrantGross. Grant's e-mail address is grant_gross@idg.com.

See more on the controversy over SOPA.