"We will not endorse anyone who won't support this reform," said Shelton.
More than 70 labor leaders, scholars, and activists contributed to a new report released last Thursday by Harvard Law, which lays out a vision for a massive overhaul of U.S. labor law.
The House of Representatives is expected to vote on the historic bill next week.
AT&T has cut over 37,000 jobs since the Tax Cut and Jobs Act went into effect two years ago.
Schleuss won the election as president of the NewsGuild-CWA in December.
