The lawsuit is part of a campaign in rich countries to make drugs companies slash prices there too after the $300bn a year industry agreed to cut the prices of medication in poor countries.
The Aids Healthcare Foundation has accused Glaxo of charging too much for its successful antiviral drugs AZT, 3TC and Ziagen.
The prices charged "exorbitantly exceed its costs of licensing, manufacturing and distributing" the lawsuit charged.
Not a legal matter
Glaxo has responded with disappointment at the way its generosity to the needy has been hijacked to back legal claims for equal treatment from people who can better afford to pay for their medicines.
"GlaxoSmithKline does not believe that litigation is the appropriate pathway to resolve matters such as these," a spokesman said.
Glaxo and many other drugs giants have agreed to slash the cost of medication in many poor parts of the world, as well as the prices of medication for other poor people such as the elderly in the US.
Their price reductions have not come merely due to the firms' altruistic nature, however.
Sometimes they have no choice but to slash prices to fend off illegal copycat products.
And in future, this battle will heat up as the patent protection awarded many of today's best selling drugs expire.
The drugs industry has consistently argued that it needs to continue charging high prices for drugs in order to pay for the research and development of new ones.
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