The Wall Street Journal reported on Tuesday that the public relations firm Berlin Rosen was hit with a subpoena as the investigation into New York City Mayor Bill de Blasio’s fundraising continues to expand.

In addition to its work with de Blasio, Berlin Rosen plays a key role in the SEIU-backed “Fight for $15” campaign, quarterbacking media operations promoting the protests from its New York City headquarters, a relationship that has paid Berlin Rosen some some $4 million since 2012.

According to SEIU’s LM-2 disclosure form, SEIU paid BerlinRosen $1.7 million in 2015. This is on top of the $1.3 million SEIU paid the firm in 2014, $848,000 in 2013 and $393,000 in 2012, as reported by Politico.

As SEIU continues to underwrite the “Fight for 15” to grow union membership and advance the liberal labor agenda, it’s telling that they are joined at the hip with a firm that’s now at the center of the growing de Blasio investigation.