Nearly 30 Democrats complained to Energy Secretary Rick Perry on Tuesday that the Department of Energy is withholding clean energy funding that Congress already designated under previously passed spending bills.

"These actions not only ignore congressional intent, but are explicitly prohibited by law," read a letter sent by Sen. Maria Cantwell of Washington state, the top Democrat on the Energy and Natural Resources Committee, and 27 of her colleagues.

They explained that the agency has either "delayed awarding funds," or, in some cases, is outright "refusing ... to release funds altogether for various activities for which Congress has already provided appropriations," according to the letter.

The senators said they are receiving complaints from academic institutions and others that the Energy Department has cut them off completely.

"We have heard from small businesses, universities, and research institutions, as well as media reports that the DOE has slowed down or frozen some of its essential research and development programs that promote American innovation, economic competitiveness, and cutting-edge science," the letter explained.

The senators cite a May 4 memo sent by Perry's chief of staff to all office heads, halting funding if it the money hasn't been obligated yet. The memo said the action was necessary in order to ensure that the department was acting in line with the "direction" of President Trump's fiscal 2018 budget blueprint. The Trump budget has not been formally proposed yet, and must be marked up and passed by Congress in order to go into effect — and even that is unlikely to happen given Republican divisions in Congress.

The letter said the senators have reason to believe that research funding under the Energy Efficiency and Renewable Energy Office, the Advanced Research Projects Agency for Energy, the Loan Office and the Science Office are all being withheld.

"Each new president certainly has the right to influence the direction of the Executive Branch. However, the President cannot ignore statutory requirements or funding direction provided by appropriations legislation for Fiscal Years 2016 and 2017," wrote the senators.

"It appears that the department may already be ignoring congressional direction," the letter added.