By Matt Murphy, State House News Service | 4 hours ago A security guard sits in front of Stem, 124 Washington St., Haverhill. (WHAV News file photograph.) Advocates, lawmakers and former regulators urged a legislative committee on Tuesday to provide more oversight of required contracts between municipalities and marijuana businesses, arguing that the system continues to be exploited by some cities and towns, which creates a barrier for small and minority owned businesses to get started in the industry. A suit against the City of Haverhill, filed by downtown marijuana retailer Stem and its president, Caroline Pineau, played prominently before the Committee. The issue of host community agreements has been one fraught with tension as people in the industry have argued for years that negotiations are often “one-sided,” with communities controlling all the leverage.