The Central Bank of Nigeria claimed that some banks were already breaching the 15% Maximum Deposit Rate rule and has warned erring institutions.  The maximum deposit rate ws imposted by the CBN and agreed to by the banking exectives on April 1 after some of the banks started scrambling to attract deposits during a liquidity squeeze driving the deposit rate over 20%:

However, in less than two weeks after the said Bankers’ Committee decision was made public, some banks have resumed the fierce competition for deposits by offering deposit rates in excess of the agreed maximum of 15 per cent per annum in order to entice depositors to move their deposits from one bank to the other.

To effectively deter and penalize actual violations of the Bankers’ Committee’s decision on maximum deposit rate, lending rate and other charges, the following sanctions shall, without prejudice to the provisions of Section 60 and 60A of BOFIA, 1991 as amended, be applied against erring banks.
i.  First Time Monetary penalty of N50 million and a letter of warning to the MD/CEO of the erring bank.
ii.  Second Time Suspension of the bank from accessing the RDAS and Class ‘A’ Bureau de Change window in addition to the fine of N50 million.
iii. Third Time Suspension of the MD/CEO, and all officials of the bank involved in the
breach.

You can read the memo here: [Download not found]