Glencore latest offer is for Teck's shareholders to receive 24% of the combined metals group and up to $8.2 billion in cash for those who may not want exposure to thermal coal, which is the most polluting fossil fuel.
Teck said its board will review and evaluate the offer, but nevertheless believes it is "largely unchanged" from the original bid.
"The revised proposal does not provide an increase in the overall value to be received by Teck shareholders or appear to address material risks previously raised," Teck said in a Tuesday statement.
"Getting Teck's Class A shareholders on board is a separate, more substantial challenge," LaFemina added.
Reuters on Monday reported that Glencore Chief Executive Gary Nagle plans to meet with some of Teck's Canadian shareholders in Toronto on Thursday to personally lobby them for support.