MUCH HAS BEEN made of how the seven-way field in Tuesday’s special election Democratic primary for the East Boston-based state Senate seat breaks with tradition in several ways. It features two minority women candidates, no lifelong Eastie resident – the usual profile of the seat holder — and a competitive candidate from Beacon Hill.

But the race appears to be living up to one less-than-proud tradition of old-school Boston politics: the last-minute attack piece.

Rizzo attack mailer
Attack fliers landed in mailboxes over the weekend in the First Suffolk and Middlesex Senate District, days before Tuesday’s seven-way Democratic primary.

Fliers landed in mailboxes across the district on Saturday accusing one candidate, former Revere mayor Dan Rizzo, of being a serial endorser of Republican candidates. “An endorsement is a statement of values,” it reads. “And Dan Rizzo endorsed Republicans like Mitt Romney, Scott Brown and John McCain.”

The flier features a grainy photograph of Rizzo standing with Brown and McCain. Another picture shows him with Romney.

The flier says, in small print, that it was not authorized by any candidate or candidate committee, but was paid for by the “Mass Values PAC.”  The return address is a post office box in the Readville section of Hyde Park.

No one could be reached from Mass Values PAC. The independent expenditure PAC reported receiving funding in the 2012 and 2014 election cycles from several labor unions. Steve Crawford, a political consultant who previously served as the PAC spokesman, said he hasn’t done work for the group for more than a year.

The weekend mailing may have run afoul of state campaign finance laws. A 2014 campaign finance reform law requires all independent expenditures made by a PAC within 10 days of a primary or general election to be electronically posted within 24 hours to the state Office of Campaign and Political Finance website. There was no record by 5 pm Monday on the office’s website of any 2016 filings from Mass Values PAC.

In the 2012 and 2014 election cycles, Mass Values PAC reported spending on mailings and ads against several Republican state legislators. The PAC’s main donors in both cycles were two unions, the Massachusetts Teachers Association and 1199 SEIU, which represents health care workers.

A spokeswoman for the MTA said the teachers union has not made any donations to Mass Values PAC in this election cycle. 1199 SEIU did not respond immediately to an inquiry asking whether it has donated to the Mass Values PAC for the state Senate race.

Rizzo’s campaign did not return a message on Monday. An online search did not immediately turn up evidence to back the endorsement claims in the mailer. The flier did not include references to any published accounts that would support the claims. A Revere Journal news story less than three weeks before the 2012 election reported that Rizzo was remaining neutral in the US Senate race between Scott Brown and Elizabeth Warren.

Outside money has been pouring into races since the Supreme Court’s Citizens United decision in 2010, which uncapped donations by corporations, unions, and individuals to independent expenditure PACs, as long they don’t coordinate spending with candidate committees.

While Rizzo was attacked with PAC spending, he has also been the beneficiary of outside spending in the race. Democrats for Education Reform has reported spending more than $24,000 to boost his candidacy. Rizzo has voiced support for raising the cap on charter schools, a move that Democrats for Education Reform strongly backs.

The group reported receiving $60,000 on April 1 to spend in the race from Education Reform Now Advocacy, a New York nonprofit. The source of the New York group’s money is shielded from view because it is a social advocacy organization, UMass Boston political scientist Maurice Cunningham wrote on Monday on the MassPoliticsProfs blog.

The 1199 SEIU PAC has reported making an expenditure of $3,364 in the Senate race on behalf of state Rep. Jay Livingstone of Beacon Hill.

Lydia Edwards, a public interest lawyer making her first run for office, has received a slew of union endorsements, including from the Massachusetts Teachers Association and 32BJ SEIU, which represents custodians and other property workers. An affiliated PAC, 32BJ United Dream Fund, based in New York, has reported $56,453 in expenditures on behalf of her run.