"Before weighing the use of military force, Congress must fully debate and consider the facts and every alternative, as well as determine how best to end the violence and protect civilians," they wrote.
The letter follows other letters from Republicans and Democrats calling on Obama to seek congressional approval. More than 100 members warned earlier in the week that the War Powers Resolution does not allow Obama to bomb Syria given that Syria poses no immediate threat to the United States.
The Democratic letter said that while human rights violations are "horrific," they "should not draw us into an unwise war."
Speaker John Boehner (R-Ohio) has called on Obama to answer more than a dozen questions about his strategy for Syria before any attack begins, and has said Obama needs to make a public case to the American people before any actions are taken.