Sen. Jim DeMint (R-S.C.) scuttled a deal between Senate Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) to start long-stalled conference proceedings on an ethics and lobbying reform package Thursday afternoon, raising an objection at the last minute even as McConnell and Reid were formalizing the agreement.

DeMint made his objection to the agreement in a phone call to the Senate floor, literally minutes after McConnell had said Republicans would drop their objections to naming conferees.

After a prolonged quorum call during which McConnell spoke with DeMint on the phone in the Republican Cloak Room, DeMint, backed by fellow conservative Sen. Tom Coburn (R-Okla.) emerged on the floor.

DeMint objected to going to conference on the bill until the Senate internally adopts a set of sweeping rule reforms, which Democrats included in the bill, even though they do not need House or presidential approval.

The objection initially prompted a terse exchange between Reid and DeMint, while a clearly unhappy McConnell looked on. But with McConnell opting to remain out of the fight, Reid used his control of the floor to launch a blistering attack on Republicans.

“Here we are, seconds from going to conference and a call comes in to the Republican cloak room. I understand the Minority Leader has a responsibility to take that … but the eyes of the nation are on us,” Reid said, adding that “to not let us go to conference on some petty issue that my friend has raised is really bad.”

Democratic firebrands — including Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.), Majority Whip Dick Durbin (Ill.) and Sen. Barbara Boxer (Calif.) — also came to the floor to launch their own attacks on DeMint and the Republicans, accusing the GOP of blocking ethics reform.

DeMint accused Democrats of attempting to essentially scrap the new rules — which put in place new restrictions on how the Senate doles out billions in earmarks — in order to ease passage of massive spending bills this year without having to abide by the rules.

“We will not have earmark reform during this year’s appropriations process. That is why this is being done,” DeMint charged on the floor, adding later that “the only reason to go to conference with [the rules] in is to take them out.”

DeMint, who has had a hold on the bill pending adoption of the chamber’s ethics rules, said that he had not been informed of the agreement. “I didn’t know they were going to do that today,” he said, although he added that he believed McConnell’s decision to enter into the agreement without his consent was a simple oversight.