"We write in bipartisan support of your announcement of the start of a ‘deliberate withdrawal’ of US military forces in Syria, and we welcome the completion of this process within the next six months", the letter said.
Senator Mike Lee, Congressmen Ted Lieu, Justin Amash, Andy Biggs, Jeff Duncan, Paul Gosar, Thomas Massie, Alexandria Ocasio-Cortez, Ilhan Omar and Bill Posey co-signed the letter.
The lawmakers said in the letter that sending US troops in Syria in 2015 was "never approved by Congress" and is "in violation of the Constitution and the War Powers Resolution of 1973".
US troops have been operating in Syria as part of an international coalition to fight the Daesh* terrorist group for about four years without the permission of either Damascus or the UN Security Council.
In December, Trump announced the withdrawal of 2,000 US troops from Syria.
*Daesh (also known as ISIS/ISIL/IS) is a terrorist group banned in Russia
