The Canadian Radio-television and Telecommunications Commission says the move is aimed at enhancing competition in the wireless marketplace.
The CRTC launched public hearings last December to see whether some wireless service providers were imposing unjust terms, conditions and discriminatory roaming rates on smaller competitors.
The regulator says it found "clear instances of unjust discrimination" by Rogers Inc. through its so-called Communications Partnership.
Rogers imposed exclusivity clauses in roaming agreements that prevented smaller service providers from using networks from any other firm, says the CRTC.
Rogers then charged some new Canadian service providers significantly higher roaming rates than those offered by other wireless service providers, said the regulator.
"Competition in the wireless industry benefits society and the economy by providing innovative communications services at reasonable prices," CRTC chairman Jean-Pierre Blais said in a statement.
"But that is only the case when true and sustainable competition is at play."
The CRTC is currently looking at the overall competitive state of Canada's wireless market and plans a public hearing on the issue in late September.
In the meantime, it has sent a letter to all Canadian wireless providers, asking them how they calculate caps on roaming fees.