Four personal injury law firms and two other businesses have filed class actions alleging the nation’s largest broadcasters have conspired to fix prices on TV advertising.

The four law firms, along with an automobile dealership in Pennsylvania and a marketing consultant in Alabama, filed six separate lawsuits after The Wall Street Journal reported last month that the Justice Department was investigating whether sales teams at Tribune Media Co., Sinclair Broadcast Group Inc. and other independent TV station owners shared information with one another. Tribune and Sinclair had planned a $3.9 billion merger, but the Federal Communications Commission raised concerns about the deal. This month, Tribune filed a $1 billion suit against Sinclair over the botched merger.