Washington, DC (LifeNews.com) -- New York Sen. Charles Schumer warned Thursday that Senate Democrats may filibuster the Supreme Court nomination of John Roberts if he doesn't provide satisfactory answers about controversial issues like abortion during his Judiciary Committee hearings that begin next week.

"As we approach the hearings, rather than feel confident that we will hear candid answers to critical questions about judicial philosophy, I am concerned that the stage is being set for Judge Roberts to refuse to answer," Schumer said.

Roberts backers have accused abortion advocates in the Senate of holding Roberts to a higher standard than the two previous nominees, Justices Ruth Bader Ginsburg and Stephen Breyer.

They say Ginsburg in particular pointed to ethics rules set by the American Bar Association as to why she shouldn't answer some questions, including ones on abortion, and potentially disqualify herself from considering future cases. The Senate approved Ginsburg's nomination on an overwhelming bipartisan vote.

Congressional Quarterly reported that Sen. John Cornyn, a Texas Republican and Roberts supporter, responded to Schumer and said, "The Senate has never forced a Supreme Court nominee to answer a check list of questions.”

This isn't the first filibuster threat Roberts' nomination has received.

Sen. Barbara Boxer, the California abortion advocate, has pledged to filibuster his nomination if he doesn't back abortion or Roe v. Wade in his interview with the Senate Judiciary Committee.

Boxer said that she will both vote against Roberts and bring Senate activity to a halt if she doesn't get satisfactory answers to her questions about Roberts' abortion views.

If he declines to answer the questions the way she wants, Boxer told reporters at a pro-abortion rally at Golden Gate University in San Francisco that she will "use all the parliamentary tools I've been given as a U.S. senator" including procedures that "make it difficult for other business to get done until we get the information we need.''

Last month, some Democratic leaders told the Washington Post they didn't think a filibuster would materialize or that those engaging in one would have enough votes to stop it.

Senate Republicans have circulated a memo showing that the White House has 56 senators who they believe will vote for Roberts, including 44 who are solid. They have 44 as unknown, but eight of those are Republicans who simply haven't made a public comment but are expected to support Roberts and nine others are Democrats who have made positive public comments about the nominee.

That leaves just 27 senators who may not support the first addition to the Supreme Court in over a decade.