Baroness Paisley has hit out at an advertising campaign by sports retailer O'Neills which helped launch the company's new store in Belfast city centre last week.
Eileen Paisley, wife of the late Rev Ian Paisley, said many Christians would take offence at a shirt being advertised for sale at the new store.
The shirt features a character from hit TV show Derry Girls, with the phrase "Sweet Suffering Jehovah".
"It is with great sadness that I write regarding an item advertised for sale in the new O'Neills sports shop opened this week by the Lord Mayor of our great capital city," said Baroness Paisley.
"I'm sure I speak on behalf of a great number of Bible-believing Christians who are broken-hearted at such a blasphemous advertisement, demeaning the Holy Name of God, and using the picture of a young lady dressed as a nun under the words 'Sweet Suffering Jehovah'.
"I am sure there are many people from the Roman Catholic Church who will also be grieved to see their religion insulted in this way."
Mrs Paisley also said the Lord Mayor should be reminded that he serves all the people of Belfast - including those of a Christian faith.
"The Lord Mayor must also remember that he is the Lord Mayor of all the citizens of Belfast and treat them all equally, whether he agrees with them or not," said Baroness Paisley.
"Modern society walks past the Cross and laughs in the face of the Son of God who 'gave His life a ransom for the many, by His death on the Cross at Calvary'.
"I would say to everyone, irrespective of religion, colour, class or creed, whether rich or poor, old or young, the thrice-holy God so sadly demeaned, stands ready with outstretched arms to receive all who call upon Him to receive them as His redeemed ones.
"The blood of Jesus Christ, God's Virgin-born Son, cleanses us from all sin."