"On the face of it, it would appear that any practice of setting different tuition fees for different passport holders could constitute discrimination on the basis of national or ethnic origin," a commission spokesman said.
"We would encourage the students affected to contact the commission to discuss this further."
Cathy Luo, 18, was shocked to be told by some providers she would have to pay a higher fee than her friend.
Miss Luo said one provider offered her a "bulk discount rate" to match her Japanese friend, only if she could bring at least two other Chinese students to enrol at the school.
"I really didn't know trying to find a price for an English language course at a school here can be so complicated," Miss Luo said in Mandarin. "I feel it is really unfair that international students are being penalised just because of where we come from, and I don't think language schools should behave like they are souvenir shop retailers trying to rip off tourists."
But English New Zealand chairman Darren Conway said it was "reasonable commercial practice" for providers to charge different rates for students from different countries.
"The ability to pay by students and the general market conditions vary from country to country."
Mr Conway, who is also chief executive of Languages International, said overseas education agents were also paid different commission rates to recruit students for Kiwi schools.
"For example, while our standard agency rate is 20 per cent, we pay 25 per cent to most of our partners in Switzerland because they are so professional, and the costs of operating in Switzerland are much higher than they are in, for example, China," he said.
Kingston's international department head, Andy Leighe, said the differing course fees based on nationality reflected the "marketing direction" his school was taking.
"One of the reasons we are offering South American and Middle Eastern students a cheaper rate is because we want to get more students from those markets," Mr Leighe said.
Education New Zealand said it did not advise what course rates should be.
DISPARITY
Fees to learn English at Kingston Institute, for a 12-week English language programme:
* $2250 - for students from China, Korea and Vietnam.
* $1500 - for those from Japan, Brazil and Saudi Arabia.