The United States was accused by medical charity Medecins sans frontiers of increasing pressure on India's new government to water down strict patent rules.
India's vast generics drug industry is a major supplier of cheap copycat, lifesaving medicines to treat diabetes, cancer and other diseases afflicting people locally and globally who cannot afford expensive branded versions.
"India has been the world's affordable drug safe-haven, the biggest source of affordable medicines," Leena Menghaney, South Asia Regional Head of Medecins Sans Frontières' (MSF) Access Campaign, told AFP.
"But now the US is trying to paint India as a rogue nation" in the area of patent law, she said in an interview.
The comments come after the US Trade Representative (USTR) announced in mid-October it was starting an additional "Out-of-Cycle Review" of India's intellectual property regime in which the nation's drug patent laws will be closely scrutinised.
The review is part of US efforts to "seek constructive engagement that will both improve IP (intellectual property) protection and enforcement in India," the USTR said on its website.
US and other global drugmakers say India's strict criteria for obtaining patents and copycat drugs industry reduces incentives to produce cutting-edge medicines.
The previous Congress government, which lost power in May, had said it would not relax the country's tough patent stance which are among the world's stiffest.
Indian law insists that drugs must "satisfy the test of novelty or inventiveness" to obtain patent protection.
But US authorities are seeking to get the new right-wing government led by Prime Minister Narendra Modi to soften India's patent rules.
"The new government must stand firm and not allow the patent regime to be dismantled. It must not be bullied," said MSF's Menghaney.
"The futures of tens of millions of patients rest on this."
Unlike many Western nations, India does not award patents for so-called "evergreening" or tweaking existing drug formulas to the dismay of multinational pharmaceutical firms which rely on such measures to extend patent lives and income stream.
Also, following a visit by Modi to Washington last month, MSF noted that the two governments promised to "establish an annual high-level Intellectual Property Working Group with appropriate decision-making and technical-level meetings".
MSF said it feared the working group would give Washington a formal platform to pressure India's right-wing government which took power in May to change its patent laws.