"Like many, we are deeply concerned about the potential consequences of a preemptive military strike on North Korea (DPRK) and the risks of miscalculation and retaliation," 18 Democratic senators said in a letter to Trump.
"Moreover, without congressional authorization a preventative or preemptive US military strike would lack either a Constitutional basis or legal authority," they said.
There were mounting reports in the past months that the Trump administration was weighing attacks to rid Pyongyang of its nuclear program.
A limited and preemptive "bloody nose" strike was reportedly discussed seriously by the US military.
"Ultimately, it is an enormous gamble to believe that a particular type of limited, preemptive strike will not be met with an escalatory response from Kim Jong Un and neither the United States nor our allies should take that step lightly," said the lawmakers, who were led by Senator Martin Heinrich of New Mexico.
The senators also expressed their concern over the vacancy of the post of the US ambassador to South Korea, stressing the importance of diplomatic leadership in that role.
Relations between Pyongyang and Seoul began thawing after top DPRK leader Kim Jong Un announced in his New Year speech that the DPRK would participate in the PyeongChang Winter Olympics.
Since then, the two sides have held several rounds of talks that help ease tensions on the Korean Peninsula.