Updated 10:56 a.m.

The two U.S. senators from Maine announced Wednesday that they will vote in favor of declassifying parts of a report on the CIA's controversial interrogation program, likely providing the votes necessary to begin the process of releasing findings of a years-long investigation to the public.

Sens. Angus King (I-Maine) and Sen. Susan Collins (R-Maine), in her Capitol Hill office on Nov. 13, 2012. (Chip Somodevilla — Getty Images)

Susan Collins, a Republican, and Angus King, an independent who caucuses with Democrats, sit on the Senate Intelligence Committee and had been considered the critical swing votes on the 15-member panel. The vote to declassify the 400-page executive summary of the 6,000-page report is scheduled for Thursday. While all Democrats on the committee are expected to vote in favor of declassification, and most Republicans are expected to vote against doing so, neither Collins nor King had signaled how they planned to vote.

But several Maine newspapers had editorialized in favor of releasing the report, and both senators were under pressure from constituents to vote in favor.

Controversy surrounding the report erupted into public view last month when Sen. Dianne Feinstein (D-Calif.), who chairs the Intelligence Committee, accused the CIA of improperly accessing materials that committee staffers were reviewing as part of their years-long investigation. The agency denied her accusations, and the matter has been referred to the Justice Department for possible prosecution.

After making her accusations, Feinstein said that she would call a vote in declassify the report. But voting to do so doesn't mean it will be immediately released to the public. First it will be sent to the CIA for a final review, a process that could take several months, if not years.

Adam Goldman contributed to this report.