This move was expected as Bell remains unsigned after the team franchise tagged the All-Pro back for the second consecutive year.
Last season, Bell stayed away from the team until September after both parties failed to reach a long-term agreement by the July 15 deadline.
This year, Bell has threatened to miss games or even retire short of an extension, a stance he has softened in recent months.
Bell could earn $14.5 million on the tag, which he considers his contractual floor for a per-year payout on a long-term deal. The Steelers have until July 16 to agree to a deal with Bell, who turned down an offer from the team this offseason.
"We're not coming to a number we both agree on -- they are too low, or I guess they feel I'm too high," Bell told ESPN in March. "I'm playing for strictly my value to the team. That's what I'm asking. I don't think I should settle for anything less than what I'm valued at."
Bell's career average of 128.9 yards per game is the highest ever for a running back over the first five years of a career.