Updated: 10:14 p.m.

Legislation to combat overseas online piracy is hemorrhaging support after recent intense opposition from major websites such as Google, with Senate Democrats and Republicans reassessing their position.

The Senate Judiciary Committee unanimously approved the bill — known as the Protect IP Act, or PIPA — last May, but it wasn’t until recently that large websites, such as the online encyclopedia Wikipedia, began to oppose the measure. Wikipedia went temporarily black today to protest the bill.

Other websites, including link aggregator Reddit, also held online strikes in an effort to raise awareness of the issue. Opponents believe the bill overreaches and would impede Internet users who do not violate copyright laws.

For example, if something on a website contained copyrighted material, the entire website could be shut down without first notifying the users or the owners of the website, opponents allege.

If enacted, PIPA and a House version of the bill would allow the Department of Justice as well as individual copyright owners to bring legal action against Internet users who post copyright-infringing content.

Senate Democratic leaders still plan to hold a vote Tuesday on whether to cut off debate and vote on whether the Senate will take up the measure, according to aides. They will need 60 votes to cut off debate and hope to entice members to vote for the package by promising an open amendment process.

But it is unclear whether they will have the votes, especially as the opposition to the measure wears down support for the proposal. The bill initially had 40 bipartisan co-sponsors, and some are beginning to abandon it.

Sen. Orrin Hatch said today he no longer backs the bill. “After listening to the concerns on both sides of the debate over the Protect IP Act, it is simply not ready for prime time, and both sides must continue working together to find a better path forward,” the Utah Republican said.

Sen. Marco Rubio, who was a co-sponsor of the bill, on his Facebook page today explained why he has had a change of heart.

“I believe it’s important to protect American ingenuity, ideas and jobs from being stolen through Internet piracy, much of it occurring overseas through rogue websites in China,” the Florida Republican said. “However, we must do this while simultaneously promoting an open, dynamic Internet environment that is ripe for innovation and promotes new technologies.

“Earlier this year, this bill passed the Senate Judiciary Committee unanimously and without controversy,” Rubio continued. “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.

“Therefore, I have decided to withdraw my support for the Protect IP Act,” Rubio said. “I encourage Senator [Harry] Reid to abandon his plan to rush the bill to the floor. Instead, we should take more time to address the concerns raised by all sides, and come up with new legislation that addresses Internet piracy while protecting free and open access to the Internet.”

Sen. Bob Menendez, also a co-sponsor, signaled a wavering in his support of the bill in its current form today.

“#NJ: I hear your concerns re: #PIPA loud & clear & share in these concerns. I’m working to ensure critical changes are made to the bill,” the New Jersey Democrat wrote on Twitter. “I’m fully committed to ensuring that any bill that passes the Senate will maintain freedom of the internet & protect intellectual property.”

Their comments came after six Senate Republicans, including Sen. Chuck Grassley (Iowa), ranking member of the Judiciary Committee, wrote to Senate Majority Leader Harry Reid (D-Nev.) on Friday urging him to postpone a vote scheduled for Tuesday on whether the Senate will take up the measure.

Also today, original PIPA co-sponsor Sen. Roy Blunt said he no longer supports the bill.

“I continue to believe that we can come to a solution that will cut off the revenue sources for foreign websites dedicated to counterfeiting and piracy that steal American jobs, hurt the economy and harm consumers,” the Missouri Republican said. “But the Protect IP Act is flawed as it stands today, and I cannot support it moving forward.”

Sen. Benjamin Cardin (D-Md.) is another co-sponsor who is seeking changes to the bill. Sen. Mark Kirk (R-Ill.) also said he opposes the bill today.

Sen. Kelly Ayotte, another co-sponsor of the bill, tweeted late tonight that she would withdraw her support as well.

“Thx 2 NHers contacting me abt #SOPA #PIPA,” the New Hampshire Republican wrote. “I’m pulling my support bc your concerns deserve consideration before Congress moves fwd.”

Correction: Jan. 19, 2012

An earlier version of this article said Mark Udall (D-Colo.) was a co-sponsor of PIPA. He is not.