Following an increase in the number of complaints of overcrowding, the South Scotland List MSP has written to Michael Matheson MSP.
In her letter, Mrs Ballantyne highlighted incidents where passengers have fainted due to the overcrowding and an instance where over 100 people were left stranded at Newcraighall.
She went on to express her concerns regarding interim action until the extra carriages are available and whether there was adequate driver training being undertaken.
She said: “Thousands of my constituents in Midlothian and the Scottish Borders use this route.
“The Borders Railway is a lifeline service and is pivotal in improving geographical mobility in the south-east of Scotland.
“This is why I have written to the Transport Secretary to seek a meeting. It is important that people across South Scotland are assured that the current levels of overcrowding will not continue.”