The survey, conducted by UMass Lowell for the Boston Herald, gives Markey 56 percent among likely voters to Gomez's 36 percent support.

He takes a similar lead among all registered voters, with 53 percent support to Gomez's 32 percent support.

Voters are split in their opinion of Gomez, indicating the barrage of negative attack ads he faced in recent weeks as the Democratic Senatorial Campaign Committee and a Democratic super PAC went on air against him have affected his campaign.

Thirty-four percent of registered voters view him favorably while 33 percent view him unfavorably.

But voters feel more positively about Markey since the last poll was conducted, in March. He now stands with 48 percent of those polled viewing him favorably, up from 31 percent.

Most polls of the race have shown Markey leading by high single digits or low double digits, with the most recent poll, released earlier this week by the Boston Globe, giving Markey a 13-percentage-point lead.

Gomez is bringing in former Sen. Scott Brown (R-Mass.) to campaign with him on Monday in hopes of a final surge in time for the Tuesday election.

The survey was conducted from June 15-19 among 608 Massachusetts registered voters, with 312 considered likely to vote in the upcoming special. It has a margin of error of plus or minus 5.6 percentage points among likely voters and plus or minus four percentage points among registered voters.