TD's will stay late at the Dáil again tonight to discuss the upcoming abortion referendum.
They're expected to vote on legislation that would make it possible to hold a public vote in May.
Speaking in the Dáil, Deputy Butler said she is in favour of giving people their say in a referendum, but that she we "won't be able to vote 'yes'" to the regulation of the termination of pregnancy by law.
"To be quite clear, I am not a member of a "pro-life" group, or the Iona Institute," she said, "I am a person who has formulated my own opinions."