House Democrats are urging the investigation of a Washington law firm and three private security companies hired to undermine political opponents of the U.S. Chamber of Commerce. In a letter to four House committees, Democratic lawmakers accused lobbying firm Hunton & Williams of using subversive tactics to smear the Chamber’s critics. Leaked emails indicate Hunton & Williams solicited private security firms Palantir Technologies, HBGary Federal and Berico Technologies to propose a strategy for weakening progressive and labor groups that have challenged the Chamber’s lobbying for some of the nation’s biggest corporations. HBGary Federal chief executive Aaron Barr, whose emails helped fuel the controversy, announced his resignation this week.