Labour has written to the minister taking issue with his claim, made at Holyrood last week, that the British Transport Police (BTP) proposal was in the SNP manifesto.
In response to a question from Labour’s Richard Leonard, Yousaf said the SNP “were elected on a manifesto promise to do what we are doing with BTP integration, and I remind the member that we got more votes than his party and the main opposition party combined. That is the rationale behind what we are doing.”
Leonard, however, said the SNP manifesto made no mention of the BTP plan.
In his letter, Leonard said: “I checked the entire contents of the SNP manifesto upon which you were elected from cover to cover. Nowhere did any such promise appear.
“It would therefore appear that you have made a factual error and in so doing misled Parliament, but more importantly you are misleading the people who elect us, including those people who work on the railway, travel on the railway and police our railway.
“Moreover, if the ‘rationale behind’ what you are doing is a manifesto promise which does not exist, then I simply do not think that you can claim a mandate for this proposed bill at all.”
Critics of the merger plan say it will make tackling cross border crime more difficult.
A spokesman for Yousaf said: “It is a longstanding and well-documented ambition of the Scottish Government to integrate the British Transport Police in Scotland within Police Scotland, which will enhance railway policing through direct access to the local, specialist and national resources of Police Scotland.
“In September 2011 the then Cabinet Secretary for Justice wrote to the Secretary of State for Transport to explore the potential for the British Transport Police in Scotland to become part of a new Scottish policing landscape, with further exchanges during 2013 following the creation of Police Scotland.
“The people of Scotland would have been in no doubt about this position when they went to the polls in May.”