US President Barack Obama has been criticized by Democrats for his plans to send dozens of Special Operations forces to Syria.
Congressional Democrats say the deployment is against Obama’s promise to end US military campaigns in the Middle East.
The lawmakers said the president must seek congressional approval for using military force in Syria.
"Regardless of my views, the War Powers Resolution requires Congress to debate and authorize the escalation of US military involvement in Syria," Democratic Senator Brian Schatz said, calling Obama’s decision to send troops into the country a "mistake."
Another Democrat, Senator Martin Heinrich, sent a letter to Obama on Friday, saying a lack of vote in Congress to authorize the use of military force in Syria would be “a total dereliction of its duties and responsibilities.”
The Democrats also warned that the deployment will risk drawing US forces into combat missions and increase pressure on Washington to enter a war against Syrian President Bashar al-Assad.
On Friday, the United States escalated its fight against the Daesh (ISIL) terrorist group in Syria by authorizing the first open deployment of military boots on the ground.
Up to 50 special operations troops will be sent to assist Kurdish and Arab forces in northern Syria, American officials said Friday. The group will be the first American boots on the ground in Syria.
The White House said the special forces will serve as advisers to the foreign-backed militants in the country.
On Friday, US Defense Secretary Ashton Carter said the deployment of special forces will put US troops in harm's way.
The newly proposed forces would reportedly work in tandem with US-allied militants and Kurdish fighters, backed by American air power, to mount an offensive on northeastern city of Raqqa, the de-facto capital of Daesh.
US secretary of state John Kerry framed the troop announcement as part of a change in strategy that included diplomatic efforts to find a political solution to the conflict.
“We are intensifying our counter-Daesh campaign and we are intensifying our diplomatic efforts to end the conflict,” Kerry said. “That is why President Obama made an announcement about stepping up the fight against Daesh.”
The new plan comes as the US, Russia, Iran and 15 other countries held an international meeting in Vienna, Austria, on Friday to resolve the years-long conflict in Syria.
The attendance of Iran, whose participation in Syria talks had previously been blocked by the US and Saudi Arabia, marks a shift that offers more hope for diplomacy.