(Reuters) -Two Republican senators have put holds on three of U.S. President Donald Trump's Treasury Department nominees over a White House effort to make it harder for companies to claim tax credits for wind and solar energy projects, according to a government document and a source familiar with the matter.

The senators, Chuck Grassley of Iowa and John Curtis of Utah, hail from states with large renewable energy industries and support federal tax credits that bring down the cost of wind farms and solar arrays.

Grassley published his announcement in the Congressional Record on Friday. A source familiar with the situation confirmed Curtis' hold to Reuters on Monday.  

In his announcement, Grassley said he was putting a hold on the Treasury nominees - Brian Morrissey, who was nominated to serve as Treasury's general counsel, Francis Brooke, nominated to be assistant secretary, and Jonathan McKernan - until he was certain the tax credit rules adhered to the law.

The senators had tried to negotiate a longer timeline for wind and solar tax credits ahead of the passage of the One Big Beautiful Bill Act, but ultimately joined Republicans in backing a final draft that phases out clean energy subsidies years earlier than planned as part of their budget megabill.  

The new law requires projects to begin construction within a year or enter service by the end of 2027 to qualify for the credits. Under longstanding Treasury Department rules, a project is considered to have begun construction after spending just 5% of project costs. 

But days after signing the legislation into law, Trump last month directed Treasury to limit that "safe harbor" provision unless a substantial portion of a facility has been built, reportedly a promise he made to conservative Republicans. The agency has until August 18 to write new rules.

"What it means for a project to 'begin construction' has been well established by Treasury guidance for more than a decade. Moreover, Congress specifically references current Treasury guidance to set that term's meaning in law," Grassley wrote. "This is a case where both the law and congressional intent are clear." 

Under Senate rules, a single senator can hold up a nominee even if the other 99 want to move forward.