The Senate approved Thursday afternoon a controversial amendment by a vote of 63-29 to require the Justice Department to open an investigation into an earmark thought to have been inserted into the highway technical corrections bill by Rep. Don Young (R-Alaska).

Ten Republicans voted in favor of the measure after Senate Minority Leader Mitch McConnell (R-Ky.) cast an “aye” vote.

Senate Democratic leaders on Thursday closed ranks behind the measure penned by Sen. Barbara Boxer (D-Calif.) to have Justice probe the earmark for a $10 million road project in Florida.

They opposed a competing amendment 49-43, by Sen. Tom Coburn (R-Okla.) to establish a bipartisan Congressional commission to investigate the origins of the earmark, which was inserted after the bill had been approved by the House and Senate. The Boxer-Coburn fight has held up the passage of the highway technical corrections bill.

Young, a former chairman of the House Transportation and Infrastructure Committee, admitted this week that an aide inserted the earmark into the highway legislation, but insisted it was done for legitimate reasons and made only technical changes consistent with the spirit of the law. The money for the Coconut Road project near Fort Myers, Fla., benefitted a wealthy land developer and campaign contributor to Young and would be reversed by the technical corrections bill.

Meanwhile, Speaker Nancy Pelosi (D-Calif.) said Thursday that the matter should be referred to the House ethics panel instead of the Justice Department.

“Congressman Young has said his staff did make this change. … It’s something the ethics committee should look at,” Pelosi said.

Furthermore, House Minority Whip Roy Blunt (R-Mo.) told reporters that sending the matter to the Justice Department didn’t make sense.

“There are clearly problems in the mechanics of what happens to legislation. … This is a Congressional problem. We ought to look at it,” Blunt said.

After nearly 24 hours of quasi-negotiations with Coburn, Boxer accused the Republican of attempting to kill the technical corrections bill, which she cast as a “mini economic stimulus package.”

Ahead of the vote, the Senate Democratic Policy Committee circulated a memo to Members’ offices questioning the constitutionality of Coburn’s bill because it would have the Senate investigate a House Member.

The memo cast the Coburn measure as a political “poison pill” and said Senate Majority Leader Harry Reid (D-Nev.) “strongly supports the Boxer amendment and strongly opposes the Coburn amendment.”