WASHINGTON – A child-care provider from Falmouth who is upset with the U.S. Chamber of Commerce’s political activity spoke Friday at a rally to pressure the powerful business group to disclose its donors.

“My message is simple: the U.S. Chamber of Commerce doesn’t speak for small business and it doesn’t speak for me,” said Melanie Collins, owner of Melanie’s Home Childcare and a member of the organization Main Street Alliance, to several dozen activists near the chamber’s headquarters.

The U.S. Chamber of Commerce has spent more than $1.3 million so far on political advertising in Maine’s U.S. Senate race — opposing independent Angus King or supporting Republican Charlie Summers — and has pledged to spend as much as $100 million nationwide on the 2012 elections.

The U.S. Supreme Court’s Citizens United ruling in 2010 opened the door for corporations and labor unions to spend unlimited amounts of money on elections.

As a nonprofit, the chamber is not required to disclose the donors behind its political activities.

That has led to allegations that corporations are funneling huge sums into the election through the chamber and other organizations, while leaving the public in the dark about who is behind the attack ads and other messages.

On Friday, representatives of several progressive organizations — the U.S. Public Interest Research Group, Public Citizen, the Business Ethics Network, Main Street Alliance and Citizens for Responsibility and Ethics in Washington — held a rally to call for stronger disclosure laws. But the primary target was the U.S. Chamber of Commerce, due in part to its stature and its opposition to attempts to require more disclosure of donors.

“They are the poster child for the unaccountable big money that is spreading secrets and lies through our democracy and corroding our right to self-government,” said Blair Bowie, an advocate for U.S. PIRG.

Politically active nonprofit organizations keep their donor lists confidential, and the U.S. Chamber of Commerce is not the largest “independent spender” in this year’s elections, although it is one of the biggest in the race to fill Maine Sen. Olympia Snowe’s seat.

Chamber officials did not respond to requests for comment on the disclosure issue Friday.

In a letter sent to senators in July, the chamber’s Executive Vice President R. Bruce Josten warned that the organization would include votes on a bill to expand disclosure requirements in its legislator scorecard.

The chamber argued that the bill would infringe on businesses’ constitutionally protected free speech and unfairly exempt labor unions, a claim disputed by supporters.

The bill failed to advance in the Senate.

In a park between the chamber’s headquarters and the White House, Friday’s rally included a mock birthday celebration — complete with cake and party hats — to mark the chamber’s 100th anniversary. The group then marched to the chamber building for a brief protest and to deliver what organizers said were 30,000 petitions calling on the organization to shed light on its political donors.

Collins, who has run her child-care center in Falmouth for 13 years, had a long list of grievances against the chamber beyond its support for Summers, the Republican candidate in Maine’s Senate race.

She criticized the chamber’s opposition to President Obama’s health care law, which she described as one of the best things to happen to her business and credited with keeping her insurance premiums stable this year. Collins is a member of the Maine Small Business Coalition ,which is the state affiliate of the Main Street Alliance, a network of small business coalitions.

“To the rich CEO they say give us your money, we’ll do your political dirty work without leaving your fingerprints on it,” Collins said. “Secrecy is not a small business value.”

The U.S. Chamber of Commerce’s involvement in the Maine Senate race has created confusion — and headaches — for local chambers that, unlike the national group, are steering clear of endorsing candidates.

In the wake of the national chamber’s anti-King ads, both the Maine State Chamber and the Portland Regional Chamber have made clear to members that they are not involved in the U.S. Chamber’s political activity.

King has considerable support in some business circles, especially in Portland and the midcoast.

Washington Bureau Chief Kevin Miller can be contacted at 317-6256 or at:

kmiller@mainetoday.com