The top Democrat on the Senate Foreign Relations Committee continued to urge President Obama to stop his attempt to undercut Congress and bring the Iran deal to the United Nations before U.S. lawmakers have a chance to weigh in.

Sen. Ben Cardin, D-Md., said he believes any attempt by the Obama administration to take the Iran nuclear agreement to the United Nations for approval first flies in the face of a measure the Senate passed earlier this year that agreed to wait until the negotiations were done before Congress went ahead with new sanctions.

"I don't know why they're going to the United Nations," he told Chris Wallace on "Fox News Sunday." "I think they should [go] to the U.N. after the 60-day review. I don't think it's consistent with the Iran Sanctions Review Act."

"There's nothing to be lost by waiting," he added.

Sen. Bob Corker, a Tennessee Republican who chairs the Foreign Relations panel and the main author of the Iran Sanctions Review Act, on Thursday accused the Obama administration of trying to outmaneuver Congress with the U.N.-first strategy. He called the effort an "affront" to the American people and Congress.

Corker and Cardin then sent a letter to Obama, urging him to reconsider. But the White House said Friday they are sticking with their plans to seek quick U.N. approval of the deal, saying it made sense to do so because the body's Security Council is made up of all the world powers that helped negotiate the deal, including the U.K., Germany, France, Russia and China.

Cardin said he is still reviewing the complicated Iran deal and has yet to make a decision on whether to support it or not.

But he stressed that his decision would not be based on party loyalty or support for Obama but instead on what's in the best interest of the United States' national security.

"My obligations are to the people of this country," he said. "[I]t's not a matter of what party I belong to, it's not a matter of supporting the president, it's what's important to this country."

Sen. John Barrasso, R-Wyo., said senators on both sides of the aisle are skeptical of the deal, especially a "last-minute concession" that would allow Russia to sell ballistic missiles to Iran in eight years.

"The concession that we would now allow Russia to sell to Iran ballistic missiles that could hit in the neighborhood but also with the strength that could hit the United States, I think was an absolute mistake and a concession, and almost a surrender by the president to get any deal," he said.

Cardin said he was mainly focused on the inspections and enforcement provisions in the deal.

"We want to look at the covert opportunities. We understand that we cannot trust Iran – that there are many ways that they can get a nuclear weapon and one is through covert activities on a military facility," he said. "What does the 24-day delay mean? And that is one of the questions we will be asking."

Senate Foreign Relations will begin holding hearings this week, he said, and that's "one of the primary areas of our interest."