Republican senators are asking where President Donald Trump came up with the money to pay more than a million military service members during the government shutdown.

On the one hand, GOP lawmakers are glad active-duty service members aren't missing their paychecks this week as the shutdown continues, but they're frustrated that Trump appears once again to be stealing their constitutional power of the purse, reported The Hill.

“I am using my authority, as Commander in Chief, to direct our Secretary of War, Pete Hegseth, to use all available funds to get our Troops PAID on Oct. 15th,” Trump posted on Truth Social. “We have identified funds to do this."

The Pentagon identified $8 billion in unspent research, testing and evaluation money to be used to pay troops during the shutdown, but some Republican senators are worried the Trump administration will raid other federal programs once those unobligated funds run out.

“That’s a concern of not just appropriators, it seems broader than that,” said one GOP senator who requested anonymity.

That Republican said GOP colleagues have asked the administration for more details about other accounts that could be used to pay troops during the shutdown and what legal authority the White House would cite to justify tapping into them.

“We’ve been given two different explanations," said Sen. Susan Collins (R-ME), the chair of the Senate Appropriations Committee. "One, is that it’s unobligated balances. One, is that it’s taken from certain research and technology programs. But we don’t have the specifics. We have asked for the specifics."

Senate Appropriations Committee Vice Chair Patty Murray (D-WA) questioned whether Trump's move to pay service members was legal.

“I do not know the answer to that question," she said.

Sen. Lisa Murkowski (R-AK) also went on record with her concerns about the president repurposing congressionally approved funding without input or approval from lawmakers.

“I get that they say for the military pay for this pay period it comes out of … research and development technology [fund] but where? Is that taking it from projects that we have already identified?" Murkowski said. "Maybe something’s really important to me. Where’s it coming from? We haven’t seen that. Typically what will happen is you’ll have some kind of reprogramming request."