Senate Majority PAC, a top Democratic super PAC, announced plans for a “major statewide buy” Thursday in the special election in Massachusetts.

“We will not stand idly by while Mitch McConnell and national Republicans try to use backdoor dollars to buy this race for [GOP nominee Gabriel] Gomez,” said Craig Varoga, senior strategist for Senate Majority PAC, in a release.

The announcement comes hours after the Democratic Senatorial Campaign Committee started buying airtime to boost Democratic Rep. Edward J. Markey. Roll Call contributing writer Stuart Rothenberg broke the news of that television buy.

The investment indicates that Democrats are nervous about Markey’s chances in the June 25 special election. Most recent polls have shown the race as a single-digit contest, but with Markey in the lead.

“Democrats have said from day one that we will take nothing for granted in this race,” the DSCC’s Matt Canter said in an emailed statement. “It’s clear that Ed Markey has a strong lead that will grow as voters learn more about Gomez’s support for the national Republican agenda.”

Kyle Trygstad contributed to this report.