Stuart Campbell, who runs the Wings Over Scotland website, is suing the Scottish Labour leader for £25,000 after she accused him of homophobia.
Ms Dugdale told MSPs at First Ministers Questions on 18 May that she had “called out” Campbell in a newspaper column she writes because of “homophobic comments” he had made about the Tory MSP Oliver Mundell.
The claims of homophobia have been rejected by the blogger.
In a statement posted online today, Mr Campbell said: “When we originally ran the Dugdale/Mundell story in May, after Dugdale had blanked an attempt to settle the matter out of court, we asked you to decide what we should do about it – whether we should bring a court case or just let it go, and whether if we pursued it we should use existing Wings funds or do a separate fundraiser.
“So we’ve done it. It’s initially for a small amount to cover the expenses that have been incurred to date in professional legal advice from counsel and filing the case, though more will likely be needed in future if and when it actually gets to court.”
The row stems from a tweet by Mr Campbell during the Tory conference in March. Mr Mundell’s father David, the Scottish Secretary, became the first serving Conservative cabinet minister to ever publicly state he was gay last year.
Mr Campbell tweeted: “Oliver Mundell is the sort of public speaker that makes you wish his dad had embraced his homosexuality sooner.”
Speaking in the Scottish Parliament in May, Ms Dugdale said: “I stand firmly by my comments. I’ve never kowtowed to a bully and I will not start today.
“There is a catalogue of evidence that demonstrates the bile that Stuart Campbell appears to believe is acceptable.”
Speaking in respone to the Scottish Labour leader’s comments, Mr Campbell said: “The tweet Kezia Dugdale read out at FMQs is – obviously – not homophobic in any way.
“It’s a criticism of Oliver Mundell’s terrible public-speaking skills, and to the best of my knowledge Oliver Mundell isn’t gay. I absolutely and categorically reject any accusations that I’m a homophobe.”
A spokesman for Scottish Labour said: “Court action has been commenced and will be robustly defended.”