About 100 union plumbers from a Boston-based local plan to knock on union members’ doors Saturday in Portsmouth, N.H., and “Joe the Plumber” is certain to be a topic of conversation, said Kevin L. Cotter, business manager of Local 12 Plumbers and Gasfitters union.

The group will be urging union members to vote for Obama and Democratic US Senate candidate Jeanne Shaheen, who is challenging John Sununu, the Republican incumbent.

“He’s impersonating a plumber,” Cotter said, referring to Joe Wurzelbacher, the Ohio man who confronted Obama about his tax plans and who became a media celebrity after John McCain repeatedly referred to him during the presidential debate Wednesday night.

Wurzelbacher, however, has paid a price for his moments of fame; news media reports have said he does not hold a plumber’s license, has been hit with a tax lien, and would probably qualify for a tax cut under Obama’s campaign proposal.

“We will definitely be talking about ‘Joe the Plumber,’ ” said Cotter, whose international union was the first to endorse Obama during his run for the Democratic nomination.

The union’s local in Wurzelbacher’s neck of the woods plans an event Sunday, timed with McCain’s visit to Toledo, to disavow Joe the plumber, too. “Actual plumbers will share their concerns with several of Senator McCain’s proposals including his plan to tax employer-based health care insurance, his tax proposal which favors the wealthy over working Ohioans and other issues that will impact working families,” the local said.