Back in October, the Screen Actors Guild-American Federation of Television and Radio Artists began a campaign aimed at the ad industry, looking to generate interest and get more non-union agencies into its fold.

That campaign targeted Droga5 and some of its own members, alleging that the agency shoots non-union work with union performers, paying them non-union wages.

Now, as new contract negotiations with the ad world approach in February (its current three-year contract expires in March), SAG-AFTRA appears to be taking its campaign a little more seriously: It's sharpening its tone and buying promoted tweets on Twitter and sponsored posts on Instagram.

The group on Monday bought a promoted tweet that ran Monday morning that said: "Fight for fair pay. Tell @Droga5 to stop exploiting actors and pay fair wages." It appears as though that tweet is what's called a promoted-only tweet: one that gets fanned out as a promoted item, but can't be viewed on the poster's newsfeed. The group's promoted items on Instagram had the same copy.

It wasn't immediately clear how much money SAG-AFTRA is putting behind the promoted campaign, or whether it bought sponsored posts on Facebook, or banner ads online. What's also unclear is how spohisticated the targeting agorithm was, or how many people in adland the messages reached. A SAG-AFTRA spokeswoman did not immediately respond to a request for comment.

The union's items on Twitter last fall were generally softer in tone:

Dear Dave @droga5 @ddroga, let's make #beautifulmusic together! #adsgounion #sagaftramember pic.twitter.com/VSUjPwWtOT

— SAG-AFTRA (@sagaftra) October 21, 2015

Droga5 has denied SAG-AFTRA's allegations of exploiting talent. "Droga5 remains a non-signatory to the SAG commercials contract, enabling us to engage in non-union shoots when it is deemed appropriate," the shop said in a statement to Ad Age on Monday. "However, when managing SAG productions, we always use SAG performers, which include any commercials for SAG-signatory clients or featuring any SAG celebrity talent. In those instances, we abide by SAG rules and pay SAG wages across the board. We do not engage SAG performers in non-union productions."

Because it is not a union agency, Droga5 can generally operate outside the industry's contract with the union, but SAG-AFTRA actors working a non-union job can face disciplinary charges.

Also on Monday, Sag-AFTRA said in a release that its members would show up at Droga5's lower Manhattan headquarters, delivering a petition that asks the agency to "stop undermining the industry standards that ensure commercial performers can earn a middle-class living."

The statement said more than 8,000 members have signed the petition. "The union will demand that Droga5 live up to its self-professed commitment to being 'humanity obsessed' by paying fair market wages for performers in all of their productions," the statement said. "Droga5's current practice of paying actors substandard wages without benefits is unfair and exploits the often struggling performers who take the jobs."

Tension between the industry and the union has sprouted up in recent years as marketers have increased demand for digital content, whether that's paid, 30-second pre-roll spots that run on YouTube or other forms of branded content like longform videos or Vine videos. Brand budgets for these pieces of work tend to be low enough that agencies say they sometimes can't afford union talent.

That demand for digital content also comes at a time when many hot shops that bloomed in the last 10 years are increasingly sought-after by advertisers and are not themselves SAG-AFTRA signatories.