In August of last year, Mittal steel signed a $900 million contract to mine Liberia's deposits of iron ore.
The deal, which was supposed to last 25 years, was signed with the country's unelected transitional government.
Liberian president Ellen Johnson Sirleaf pledged to review it when she took office early this year. Talks to renegotiate began in September and are expected to conclude this week in New York.
Patrick Alley with London-based rights group Global Witness says the original deal with Mittal allowed the company to avoid paying royalties to Liberia on what it mines.
"It is quite standard that a multinational would try to limit their taxes," he said. "But in this case it is doing it directly at the expense of one of the poorest countries in the world. That is our major objection."
The agreement also gave Mittal control of railroad lines and exempted the company from certain labor laws.
Netherlands-based Mittal could not be reached for comment but has said the deal is a key part of its expansion plans. Mittal is the world's largest steel company.
Liberia is still recovering from a 14-year civil war that ended in 2003. Government officials hope a renegotiated deal with Mittal will create badly needed jobs and spur economic development.