Several U.S. farm and consumer groups are working on strategies to derail a proposed tie-up of Monsanto Co. and agricultural seeds and chemicals rival Syngenta AG, saying a combination of the market leaders would spell fewer and higher-priced products.

Coalitions of opponents are being formed and market analyzes being done, moves that underscore the hurdles U.S.-based Monsanto will face in any deal to take over Swiss-based Syngenta.

"We will aggressively oppose it," said Roger Johnson, president of the National Farmers Union. "This would reduce competition in the marketplace that is already highly concentrated."

Monsanto, the world's largest seed company, has yet to persuade Syngenta, the world's top provider of agricultural chemicals, to even start negotiations.

But Monsanto says it is making progress persuading Syngenta shareholders that its $45 billion acquisition offer should not be ignored. It says the deal would win regulatory approval despite market concerns.

Monsanto spokeswoman Sara Miller said farmers would benefit through greater product innovation. "Farmers remain our No. 1 priority," she said. "That will not change."

The NFU is one of several groups in a loose coalition that is on working the objections it will present to the Justice Department if a deal comes together. The Food & Water Watch consumer advocacy group is doing a market analysis on which to base its objections.

The American Antitrust Institute nonprofit group also will lobby against any deal. Diana Moss, its president, said Monsanto's stated intention of selling off Syngenta's seeds and traits businesses is a "red herring," and that the combined company would be a dominant player in the key agricultural platforms of seeds, genetic traits and crop chemicals.

"Farmers are already paying through the nose," Moss said. "This would take it to a whole new level."

Some individual farmers are also making their opposition clear.

"I hope they don't get it done," said Ohio farmer John Davis, past president of the Ohio Corn and Wheat Growers. "They could get to the point where they could charge whatever they want."

Large soybean and corn grower groups are not taking an official position yet as they wait to see the details of any deal. But they say they have concerns.

The National Corn Growers Association met with Monsanto leaders to discuss the proposed merger in mid-July.

The group appreciates Monsanto's "transparency," but will seek an independent analysis of the merger's market impact, Chief Executive Chris Novak said.