WASHINGTON (AP) — Fourteen Democratic members of Congress are voicing opposition to authorizing unilateral U.S. sanctions against Venezuela ahead of a House vote Wednesday.

The bill instructs the Obama administration to compile a list of human rights abusers in the Venezuelan government, freeze their assets and ban them from the United States. Foreign relations committees in the House and Senate have overwhelmingly approved it.

Administration officials are opposed. They say sanctions risk undermining mediation efforts in Venezuela and straining relations between the U.S. and Latin American partners.

The Democrats led by Michigan Rep. John Conyers wrote a letter to President Barack Obama Tuesday backing his administration. They also urged an exchange of ambassadors with Venezuela after a four-year hiatus.

Violent unrest has gripped Venezuela for months. Forty-two people have been killed since February.