Sen. Tom Coburn (R-Okla.) is threatening to withhold support for legislation making technical corrections to the 2005 highway bill if it does not require a “full and open” investigation into the now-notorious Coconut Road earmark.

Coburn wrote a letter to Senate Minority Leader Mitch McConnell (R-Ky.) Tuesday informing him that he would object to any effort to “hotline” the technical corrections bill if it did not include language calling for the appointment of a select committee to probe an unorthodox change to an earmark made after both chambers passed the highway bill but before it reached President Bush’s desk.

“Because secret, improper and unauthorized changes to congressionally passed legislation call into question the integrity of our entire constitutional and legislative process, I believe a full and open investigation into this matter is necessary to restore the integrity of both the U.S. Congress and the Constitution,” Coburn wrote.

Coburn acknowledges that the latest version of the technical corrections bill reverses the change to the original language, which authorized the money for “widening and improvements” for I-75, but he argued that more must be done.

“Those who perverted and distorted the explicit will of the U.S. Congress must also be held to account,” he wrote.

The offices of McConnell and Reid did not respond by press time to a request for comment.

The controversy surrounding the earmark has lingered for months as Republicans struggled to find a vehicle to reverse the change. According to the Congressional Research Service, such a substantive change to a bill can be made only through a concurrent resolution, something that did not take place.

The change in the transportation bill caught the attention of members of Florida’s Lee County Metropolitan Planning Organization, who were counting on the road-widening money and were alarmed when it was redirected to Coconut Road. They have since voted three times to send the money back to Congress in the hope that the funds would be reallocated for their original intention.

Watchdog groups have charged that Rep. Don Young (R-Alaska) initiated the change to benefit a number of Florida developers. Taxpayers for Common Sense (TCS) asked the ethics committee to investigate whether Young was motivated to request the change following a $40,000 fundraiser held for him in the Southwest Florida district. One of the developers who helped organize the event, David Aronoff, owns 4,000 acres adjacent to Coconut Road, including 1,200 acres directly east of the proposed interchange.

Young has refused to say whether he initiated the change. But he has argued that local residents and Florida’s Gulf State University requested the money for Coconut Road to provide hurricane evacuation routes.

In response to Coburn’s demand for an investigation, Young spokeswoman Meredith Kenny said: “Rep. Young has consistently welcomed an open earmark process.”

Since the controversy began, there has been constant finger-pointing between current and former House GOP Transportation Committee staffers over who was responsible for requesting the earmark change from the House enrollment clerk. Coburn spokesman John Hart said his boss intends to provide the investigative committee with subpoena power to ensure a strong and thorough probe, although the language is not yet finalized or agreed to.

Keith Ashdown, vice president of policy for TCS, applauded Coburn’s tough stance.

“It’s unfortunate that any one senator has to call for an investigation in a bill because the ethics committee is a toothless tiger,” he said.

Ashdown added it is well within Coburn’s right to call for a probe because the improper change in the transportation bill was made outside both the House’s and Senate’s legislative process. If one committee is allowed to do it, he said, others will try.

Members of the House Transportation Committee are distressed by the move to place yet another hurdle before a bill that has languished in the Senate under the threat of holds. Sen. Jim DeMint (R-S.C.) has threatened to put a hold on the bill because of several provisions in it, including a generous increase for a light rail project spanning from Las Vegas to California, which is a pet project of Reid’s.

In early October, Rep. John Mica (R-Fla.) and House Transportation panel Chairman Jim Oberstar (D-Minn.) agreed to work on making the change to Coconut Road in response to a request by Rep. Connie Mack (R-Fla.), who represents Lee County. Earlier this month, Mica was optimistic that a final bill would pass and be signed into law in December.

Mica’s office did not respond to a request for comment by press time. But Oberstar’s office was clearly disappointed by Coburn’s decision to up the ante just as his office was feeling like work had finally wrapped up on the corrections bill.

“We’ve been working on this bill for a very long time and Congressman Oberstar does not want to see anything else hold it up,” said Jim Berard, his committee spokesman.

Berard said he believed that Senate leaders have now changed their plans and will bring the bill up under regular order. Such a strategy would require 60 votes to reach cloture on the measure and avoid a lengthy debate on some of its controversial projects.

When asked whether his boss supports an investigation into the Coconut Road earmark change, Berard said: “That’s not something we had any part in.

“If there is a need for an investigation of some sort, either by the ethics committee or someone else, that’s something for the leadership to deal with,” he continued. “Congressman Oberstar wants to see this bill move and doesn’t want to see anything extraneous get in its way.”

The offices of House Speaker Nancy Pelosi (D-Calif.) and Minority Leader John Boehner (R-Ohio) did not immediately respond to a call for comment on the matter.