The U.S. Capitol is seen in early morning light in Washington, Tuesday, Dec. 31, 2013. A two-year, $60 million renovation of the U.S. Capitol dome has begun inside the dome, with exterior scaffolding expected in the spring of 2014. (AP Photo/Jacquelyn Martin)

The U.S. Senate could soon force its members to electronically file their campaign finance reports, but most senators remain unwilling to instantly disclose their political dollars, according to a Center for Public Integrity review of Federal Election Commission filings.

Only 21 senators — a bipartisan group that ranges from Sen. Thad Cochran, R-Miss., to Sen. Elizabeth Warren, D-Mass. — voluntarily e-filed unofficial copies of their second-quarter campaign finance reports to the FEC by Tuesday's deadline. The reports covered funds raised and spent between April 1 and June 30.

Unlike presidential hopefuls, U.S. House candidates and political groups, Senate candidates file campaign finance reports on paper with the Secretary of the Senate. That office, in turn, scans them and forwards them to the FEC, which then pays a private contractor to manually input data the reports contain.

The process costs taxpayers about $500,000 each year, according to the Congressional Budget Office. The most reliable way to immediately view the senators' reports upon their filing? Physically view paper copies at the U.S. Capitol.

Sen. Jon Tester, D-Mont., has sponsored bipartisan legislation that would change that.

And in June, Tester's bill — known as the Senate Campaign Disclosure Parity Act — was incorporated into an appropriations bill, which was favorably reported out of committee, as the watchdog organization Citizens for Responsibility and Ethics in Washington previously noted.

Tester spokeswoman Marnee Banks said she was "hopeful" that the disclosure language would remain part of the appropriations bill as it moves forward.

"Sen. Tester sees the appropriations process as a way to move a bill that increases transparency, brings the Senate into the 21st century and saves taxpayers' money," Banks added.

A floor vote on the appropriations legislation has not yet been scheduled.

In addition to Tester, Cochran and Warren, senators who e-filed their second quarter reports include:

Mark Begich, D-Alaska

Barbara Boxer, D-Calif.

John Cornyn, R-Texas

Joe Donnelly, D-Ind.

Dianne Feinstein, D-Calif.

Al Franken, D-Minn.

Kirsten Gillibrand, D-N.Y.

Martin Heinrich, D-N.M.

Tim Johnson, D-S.D.

Angus King, I-Maine

Patrick Leahy, D-Vt.

Claire McCaskill, D-Mo.

Jack Reed, D-R.I.

Bernie Sanders, I-Vt.

Chuck Schumer, D-N.Y.

John Walsh, D-Mont.

Sheldon Whitehouse, D-R.I

Ron Wyden, D-Ore.

While this bloc of e-filing senators represents only about one-fifth of the Senate, its membership has more than doubled in size from mid-2011, when only nine senators electronically filed copies of their campaign finance reports.

More stories in the Primary Source blog from the Center for Public Integrity.

This story was originally published by The Center for Public Integrity, which is a nonprofit, nonpartisan investigative news organization in Washington, D.C.

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