The Government Accountability Office (GAO) will launch an investigation into Interior Secretary Ryan Zinke Ryan Keith ZinkeTrump extends Florida offshore drilling pause, expands it to Georgia, South Carolina Conspicuous by their absence from the Republican Convention Trump flails as audience dwindles and ratings plummet MORE's alleged threat against Sen. Lisa Murkowski Lisa Ann MurkowskiMomentum growing among Republicans for Supreme Court vote before Election Day Collins: President elected Nov. 3 should fill Supreme Court vacancy Barrett seen as a front-runner for Trump Supreme Court pick MORE (R-Ak.) to withhold Interior support for Alaska if the she did not support the GOP ObamaCare repeal and replace bill.

Democratic Reps. Frank Pallone (D-N.J.) and Raul Raúl Grijalva (D-Ariz.) had requested the top government watchdog look into the matter. Ethics experts say it's highly inappropriate for a Cabinet-level government agency to threaten to withhold economic development based on votes from a given state's lawmakers.

Murkowski ultimately voted against the Republican-controlled Senate's healthcare plan, which drew a tweeted complaint from President Trump.

"Senator @lisamurkowski of the Great State of Alaska really let the Republicans, and our country, down yesterday," Trump tweeted in July. "Too bad!"

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The GAO probe, reported by The Washington Examiner, comes after Interior's Office of Inspector General (OIG) closed its own investigation when Murkowski and her Republican Alaskan colleague Sen. Dan Sullivan Daniel Scott SullivanHillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll Republican Senators raise concerns over Oracle-TikTok deal Alaska group backing independent candidate appears linked to Democrats MORE, who first reported the Trump administration's threat, refused to participate

“The OIG has conducted a preliminary review of this matter, including investigative and jurisdictional considerations, and concludes that further investigation would prove unproductive,” Interior’s Deputy Inspector General Mary Kendall wrote last week.

Sullivan told The Alaska Dispatch News in August that Zinke said he would withhold department support for Alaska if Murkowski did not support the legislation.

Sullivan called the the alleged conversation "troubling."

Zinke has brushed off the claim, calling it "laughable."

"I talk to Sen. Murkowski and Sen. Sullivan all the time,” Zinke said, according to E&E News.

“A lot's been said about a lot of things. But I talk to them all the time. We get along well," he said adding "The moon has been characterized as a threat, too, so I think it's laughable."