Scotland's largest council is to be investigated by the Equality and Human Rights Commission over equal pay.
The watchdog will use its investigatory powers for the first time in Scotland to see if the council is treating pupil support assistants fairly.
More than 700 staff are believed to be affected. Glasgow City Council said its pay structure treated people equally.
Earlier this month six female council staff started a test case on equal pay at an employment tribunal.
The commission said it would investigate whether the council's pay and grading arrangements provided equal pay for pupil support assistants.
It said the action had been taken as it "suspects" the arrangements in place do not comply with "the legal requirements of the Equal Pay Act, the statutory code of practice on Equal Pay and the EHRC guidance on job evaluation schemes free from sex bias".
The commission said it was "particularly concerned that the job evaluation process adopted by the council may be discriminatory".
This was "because it does not appear to measure equally the significant features of both female and male jobs and therefore may continue to undervalue the type of work traditionally done by women".
Scotland commissioner, Morag Alexander, said: "The commission launches this investigation to identify if the council is acting unlawfully.
"However, this enforcement action also emphasises the importance of addressing the undervaluing of women's work through non-discriminatory pay and job evaluation systems.
"The issue at the heart of this investigation is about ensuring equal pay for the future through a fair, transparent and non-discriminatory pay and reward system."
A spokesman for Glasgow City Council said: "Our pay and grading structure treats people equally.
"However, it would be inappropriate for us to comment further as these matters are currently the subject of an employment tribunal."
Alex McLuckie, from the GMB union, welcomed the commission's decision to investigate.
He said the pay and grading system which the city council had introduced in 2007 was against GMB's advice.
"We told our members at the time that we thought it was discriminatory and that is why GMB has been pursuing over 700 equal pay claims for our women members against this council," he said.
"Glasgow should now do the sensible thing by paying what they owe their women employees."
The investigation is expected to be complete by the end of the year.