Just days after Boston mayoral candidate Martin J. Walsh swore off negative mailers sent on his behalf by outside groups, another piece of literature attacking his opponent John R. Connolly was dropped in the mailboxes of some Boston voters.

The new piece of literature, a two-sided color mailer paid for with labor union money, calls Connolly a “son of privilege” and alleges that he “does not understand working-class people.”

The new mailer also mischaracterized the Nativity Mission School, where Connolly taught for two years after college, as a “elite New York private school.”

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The now-closed school was housed in converted red-brick tenement, with three floors of classrooms and one floor of housing for teachers. The school focused on teaching at-risk black and Latino youth—primarily immigrants—and was funded largely by Jesuit donors.

Walsh, a union president, had previously called such language out of line and asked outside groups that support him to not attack Connolly’s upbringing.

The mailer was sent separately by two groups, the Greater Boston Labor Council, a federation of 154 local unions, and Working America, the political arm of the AFL-CIO.

In a statement Tuesday evening, the Labor Council said that in the future, its “communications to union members will focus exclusively on Martin J. Walsh’s sterling record of support for Boston’s working families. We intend to highlight why we believe he is the right choice for mayor of Boston.”

“Once again, super PACs and special interest groups supporting Marty Walsh have resorted to personal smear attacks on John and his family, and Marty Walsh is doing nothing to stop them.” said Natasha Perez, a Connolly campaign spokeswoman.

To date, there has been no evidence of outside pro-Connolly groups sending out negative mailers attacking Walsh.

Asked about the new mailers, the Walsh campaign reiterated its opposition to them.

“Marty has already spoken against such campaigning,” Kate Norton, a Walsh campaign spokeswoman, said in a statement. “He has always run on his record and on the issues facing Boston’s families. That is what he will continue to do in this campaign.”

According to election laws, outside special interest groups and labor unions can spend an unlimited amount of money on behalf of a political candidate as long as there is no coordination between the groups and the campaign.

These “independent expenditures” are often used on mailers, television advertisements, and paid canvassers.

Records show that outside groups funded by labor—including Working America—have spent almost $1.3 million on Walsh’s behalf, in addition to $410,000 given directly to his campaign.