The accusation came after a report showed money paid in grants to students with the lowest family incomes fell by nearly 3% last year, from £103.4 million in 2011/12 to £100.6m.
The figures, published by the Student Awards Agency for Scotland (SAAS), also show the number of students receiving such awards fell by 2.8% from 55,685 to 54,130 in the same period.
Overall, the funding provided to Scottish students in loans and grants together has increased by nearly £10m from £244m in 2011/12 to £254m in 2012/13.
The SAAS figures show the average support per student increasing by 1.4% to £4316, up from £4256 in 2011/12, while the number of students supported has increased from 133,990 to 135,375, a total of 1%.
Kezia Dugdale, education spokeswoman for the Scottish Labour Party, accused the Scottish Government of refusing to accept its failings on the issue of student support.
She said: "While the SNP celebrate more students receiving loans, it is concerning that the amount of support being paid out to our poorest young people going into higher education has fallen.
"Our biggest challenge is encouraging our young people from the poorest backgrounds to go into higher education.
"Scotland lags behind the rest of the UK in this and these figures do nothing to change that poor record."
Liam McArthur, education spokesman for the Scottish Liberal Democrats, said: "The SNP once famously promised to dump student debt yet these figures show they are actually putting up student debt, while at the same time cutting bursary support.
"Funding for the two bursary awards designed to support students from the poorest backgrounds has either stagnated or dropped.
"With no indication of additional funding being made for bursaries, questions remain over how effective the Scottish Government's efforts can be in seeking to widen access."
However, the Scottish Government said it was "untrue" to claim the support being paid out to the poorest young people going into higher education had fallen.
A spokesman said: "The reality is that the number receiving support is essentially static - at around 25,000 - but the average amount they receive is up significantly."
"This is before the increase in support we announced for next year of a further £250 per year - an above inflation increase.
"It is little wonder that NUS Scotland themselves have described the support here in Scotland as the best in the UK."
Michael Russell, the Education Secretary, also defended the SNP's record pointing to the fact that Scottish students don't pay tuition fees.
He said: "In Scotland we have access to university based on the ability to learn, not the ability to pay."
Gordon Maloney, president of NUS Scotland, said: "While we'd prefer these increases to come in the form of bursaries rather than loans, and will still be arguing for more, it's significantly better than no increases at all.
"Student hardship, and not having enough money to live on, is one of the largest deterrents to starting and staying at university.
"Students need to have enough money so they can concentrate on their studies, but too often they must take on multiple part-time jobs or go deep into commercial debt to avoid dropping out."
The figures also showed there were 13,385 EU students supported in 2012/13, 10% of the total number of students supported by SAAS, receiving a total of £25m in support or 4.3% of the total support paid.