T-Mobile has been ordered to prove it didn’t lie to government regulators about its 3G shutdown plans to win approval for its Sprint merger.

In a ruling by the California Public Utilities Commission (CPUC), T-Mobile is ordered “to show cause why it should not be sanctioned by the Commission for violating Rule 1.1 of the Commission’s Rules of Practice and Procedure for false, misleading, or omitted statements.”

CPUC accuses T-Mobile of making false statements...