Girlguiding Scotland has said it is "disappointed" that the Scottish government is not supporting a legal guarantee of free period products.
The organisation said it believed a new law would have helped end the stigma around periods.
Minister Aileen Campbell has said "legislation is not required".
Labour MSP Monica Lennon said it was "deeply disappointing" that the government would not back a bill she proposed on the issue.
In a statement, Girlguiding Scotland said: "We believe making free period products easily available to everyone who needs them will not only create economic benefits to individuals and families, but will also support girls and young women's participation in education and extracurricular activities, and help to end the stigma around periods.
"Creating a legal right to access period products is vital to ensure the progress already made in this area is built upon and that future governments cannot undo the welcome work that has already been undertaken."
It also urged ministers to reconsider, and called on MSPs to back a bill which would "help to create a more gender equal future".
Costs of £24m
Explaining the government's decision not to back the proposed legislation, Ms Campbell told the Scottish Parliament that universal provision of period products could cost in excess of £24m.
She said free period products were available through secondary and primary schools across Scotland and in all 19 universities and 26 colleges.
She added that the Scottish government also provided funding of £2.8m to "hundreds of community groups to provide free products.
"We do believe we are beginning to see a culture change and there is a risk that introducing legislation now would encourage people to meet only minimum standard, compared to what we are seeing in the public, private and third sectors, where organisations are going above and beyond."
But Ms Lennon said the lack of government support was "deeply disappointing".
She said: "This is a U-turn on SNP policy that I hope will be reconsidered.
"Many women and girls are still being referred to food banks and charities to get the period products they need despite the welcome action from the Scottish government to introduce free provision in schools and other community settings.
"Others are falling through the gaps and continue to experience period poverty."