The State Ethics Commission should take a second look at an opinion that could force state Senator Dan Wolf to end his campaign for governor and leave the Legislature, the head of a government watchdog group said Monday. Pam Wilmot, executive director of Common Cause Massachusetts, said that while her group supports tough ethics laws and holding government officials accountable, Wolf’s case may warrant an exemption. Wolf, a Harwich Democrat, is a founder of Cape Air and owns a 23 percent stake in the Hyannis-based regional airline. The commission told Wolf in an opinion this month that he was in violation of state ethics law because Cape Air has contracts with Logan Airport, which is operated by the Massachusetts Port Authority. Wolf suspended his gubernatorial campaign last week and said he would quit the Senate Thursday if the decision was not reversed. ‘‘We want the Ethics Commission to be very strong, but we don’t want it to be overly broad, either,’’ Wilmot said.