BOSTON (AP) — An upcoming special election for a Massachusetts Senate seat is getting plenty of attention from leaders of both major parties.

Rep. Michael Brady, a four-term Brockton Democrat, and Rep. Geoff Diehl, a three-term Republican from Whitman, are vying to succeed Democratic Sen. Thomas Kennedy, of Brockton, who died in June. A little-known independent, Anna Raduc, of Halifax, will also be on the Nov. 3 ballot in a district long dominated by Democrats but where Republicans see an opening to build on momentum from Gov. Charlie Baker's election a year ago.

Democratic party officials have branded Diehl a "tea partier" with a "right-wing ideology," suggesting he's too conservative even for many Massachusetts Republicans. The GOP, in turn, has taken to calling the Democrat "bad news Brady," and argues that he's beholden to labor unions and other special interests.

The outcome likely won't have much immediate impact in the 40-member Senate, where there are currently only six Republicans — well below the number needed to form an influential voting bloc. But a win by Diehl could easily provide a spark for the GOP heading into 2016 when all 200 legislative seats will be up for grabs.

The race could also provide an indication of whether Baker's continued statewide popularity might begin rubbing off on other Republican candidates. There has been little evidence of any coattail effect for other GOP governors in recent state history when it comes to the Democratic-controlled Legislature.

The district encompasses Brockton, a blue-collar city of about 95,000 residents, the smaller surrounding towns of Halifax, Hanover, Hanson, Plympton and Whitman, and portions of East Bridgewater and Easton. Baker carried the district over Democrat Martha Coakley last November.

Diehl likely must win large margins in the towns to overcome Brady's perceived advantage in Brockton, where he served on the school committee and city council before winning a seat in the House.

Diehl last year helped spearhead a successful ballot question that repealed a state law indexing the gasoline tax to inflation. He was also among the leaders of a proposed ballot question that would have blocked public funding for the Olympics, an effort rendered moot by Boston's withdrawal from the 2024 bidding.

Diehl dismissed the claim that he is aligned with the tea party as a desperate, Washington-style ploy by Democrats fearful of losing the seat.

"Would Charlie Baker ... the most popular governor in the country right now, endorse somebody who was considered radical?" he asked, adding that Baker called him after Kennedy's death and asked him to consider a run.

Diehl said he has work alongside liberal Democrats in the past on issues such as foreclosure protection and preventing corporations from seeking offshore tax shelters.

"I'm trying to find the best ideas from either side of the aisle," he said.

Brady declined to say whether he agreed with his party's characterization of Diehl.

"I can't always be in step with what the Democratic Party is saying," Brady said. "I'm just focused on my own campaign."

Like Kennedy, who represented Brockton in both the House and Senate over a lengthy political career, Brady heavily touts his backing by organized labor. He also cites an ability to deliver key state funding to his district for a variety of projects.

"I have always been out there with a strong voice for working people," Brady said.

Republicans have called Brady out for being the only House member of either party to vote in July against a compromise $38 billion state budget that included a provision giving the cash-strapped Massachusetts Bay Transportation Authority more flexibility to privatize some functions. The measure was strongly opposed by unionized MBTA workers.

Brady and other critics of Diehl's push to abolish gas-tax indexing contend it removed badly needed revenue that would have gone toward fixing the transit system and other crumbling state transportation infrastructure. Diehl countered by pointing to a finding from an MBTA review panel that T management had failed to spend $2.2 billion in authorized capital funds.

The Republican has gotten under the skin of his own party in the past. In March, House Minority Leader Brad Jones told the Boston Herald that he removed the lawmaker from a key committee assignment because Diehl was difficult to work with. Diehl responded that his loyalty lies with those who elect him, not with Statehouse "power brokers."