Ms Dugdale accused the SNP and Tories of being “reckless” with the Union as she renewed calls for a federal UK.
Her party wants a “people’s constitutional convention” to decide on a new political settlement for the whole country, and a new Act of Union, with increased powers for Holyrood, Cardiff Bay, Stormont and the English regions.
Ms Dugdale, who will give a speech on Scotland’s post-Brexit future to the David Hume Institute later this month, said now was the time to act to “safeguard” the Union.
She said: “In 2014, we saved our Union and I was proud to be part of a campaign that stood up for Labour values of solidarity and co-operation.
“But 2016 saw the UK put at risk once again. The reckless actions of Ruth Davidson’s Westminster colleagues led to a Brexit vote that created the divisions in our society that Nicola Sturgeon thrives upon.
“With the Tories pursuing a hard Brexit, and the SNP pursuing independence, these two parties of government are stretching the Union to breaking point.”
SNP MP Tommy Sheppard said: “Kezia Dugdale and her party should be helping the SNP to fight today’s battles.
She could join us in supporting the Scottish Government’s plan for Scotland in standing against the biggest threat to Scotland’s prosperity and the biggest concern for families – business and educational institutions right now – a hard Brexit which risks our membership of the single market.”
Scottish Conservative MSP Murdo Fraser said: “Labour are extremely late to the party when it comes to prioritising the Union.”