More than 100 House Democrats told Defense Secretary Jim Mattis on Thursday he should not send additional military personnel to the U.S.-Mexico border.

A handful of ranking members from related House committees and 104 rank-and-file Democratic lawmakers sent the top Pentagon official a letter Thursday to say, first and foremost, they do not approve of the operation, and then to ask what it will cost the government.

"We are writing today to express our opposition to the decision to use additional troops on the southern border to assist U.S. Customs and Border Protection," the letter states.

"The use of military personnel, however, will not help us meet this challenge and only exacerbates the potential to unnecessarily escalate the situation. This effort is nothing short of a militarization of the southern border to score political points and stoke misleading fears among Americans regarding immigrants," the group said.

House Armed Services Ranking Member Adam Smith of Washington, House Homeland Security Ranking Member Bennie G. Thompson of Mississippi, House Judiciary Ranking Member Jerrold Nadler of New York, and House Oversight and Government Reform Ranking Member Elijah E. Cummings of Maryland led the effort.

The group asked Mattis to share how much the deployment of the 5,200 troops — in addition to the current deployment of 2,100 National guardsmen — will cost, as well as if they will be active-duty, National Guard, or Reserve.

Democrats also asked how long the Defense Department expects this latest operation to last, and what the rules of engagement will be if they interact with people attempting to illegally enter the country and migrants in the caravan that is headed for the U.S.

"Congress was recently notified that the Administration is sending an additional 5,200 troops to the border without a long-term plan or an analysis of the effectiveness of previous deployments from this year," they wrote. "This use of military personnel and resources for functions outside of core mission areas warrants additional Congressional oversight."

The letter writers suggested a briefing to discuss the questions rather than a letter in response.