Actor Patrick Stewart says people are incorrect to assume that because he supports the right of a couple to refuse to make a pro-gay marriage cake that he's opposed to gay rights.

The Equality Commission for Northern Ireland (ECNI) last week fined the Ashers Baking Company £500 for refusing to make a cake featuring Sesame Street's Bert and Ernie with the caption “Support Gay Marriage” and the logo for QueerSpace, a Belfast-based LGBT rights group. Currently, gay couples cannot marry in Northern Ireland.

Appearing on BBC's Newsnight, Stewart defended the owners – Colin and Karen McArthur, who plan to appeal the ruling – saying that he backs their right “to say no.”

It was not because this was a gay couple that they objected. It was not because they were going to be celebrating some kind of marriage or agreement between them. It was the actual words on the cake that they objected to,” Stewart said.

They found them offensive. I would support their right to say 'no, this is personally offensive to my beliefs and I will not do it.' I felt bad for them that it cost them 600 quid, or whatever,” he added.

In a Facebook post, an angry Stewart responded to criticism of his support for the McArthurs.

As part of my advocacy for Amnesty International, I gave an interview on a number of subjects related to human rights, civil rights and freedom of speech,” Stewart explained. “During the interview, I was asked about the Irish bakers who refused to put a message on a cake which supported marriage equality, because of their beliefs. In my view, this particular matter was not about discrimination, but rather personal freedoms and what constitutes them, including the freedom to object. Both equality and freedom of speech are fundamental rights – and this case underscores how we need to ensure one isn't compromised in the pursuit of the other. I know many disagree with my sentiments, including the courts. I respect and understand their position, especially in this important climate where the tides of prejudices and inequality are (thankfully) turning.”

What I cannot respect is that some have conflated my position on this single matter to assume I'm anti-equality or that I share the personal beliefs of the bakers. Nothing, absolutely nothing, could be further from the truth. I have long championed the rights of the LGBT community, because equality should not only be, as the people of Ireland powerfully showed the world, universally embraced, but treasured.”

(Related: Patrick Stewart jokes about being falsely outed as gay.)