Washington (CNN) An environmental group on Monday called on the Securities and Exchange Commission to investigate possible insider trading involving a mining company that is pursuing a massive gold and copper mine in Alaska near the world's most valuable salmon fishery.

Earthworks, a Washington-based advocacy group, sent a letter of complaint to the SEC, the New Jersey Bureau of Securities and the Financial Industry Regulatory Authority, detailing a flurry of stock trades and communication related to Northern Dynasty Minerals Ltd. in the days prior to recent decisions by Environmental Protection Agency that were beneficial to the mine.

The company's stock price shot up after both EPA decisions were publicly announced this summer, records show.

A company spokesman for Northern Dynasty denied any wrongdoing by company officials and called the allegations "entirely false and without merit."

The so-called "Pebble project," which is slated to be built near Bristol Bay, southwest of Anchorage, is highly controversial because of its potential to damage rivers, creeks and lakes. Some 35 million wild sockeye salmon return to spawn every year in those waters, making it one of the world's last untrammeled salmon runs of its kind.

Under President Barack Obama, the EPA in 2014 took the unusual move of putting a special protection on the sensitive watershed, making it almost impossible for Northern Dynasty, the mine's Canadian parent company, to get a mining permit.

That all changed on June 26 when the Trump administration's EPA announced it was reconsidering the special protection and essentially beginning the process to remove the protection . On July 30 the EPA announced the final lifting of the Obama-era restrictions.

The precise timing of the June 26 announcement was a surprise; even top EPA scientists and agency insiders who have long worked on the Pebble Project told CNN they were caught completely off guard.

While EPA's employees may have been surprised by the announcement, Earthworks' complaint points to a dramatic rise in the volume of Northern Dynasty stock trades in the week before.

"We believe what happened is that inside information was disclosed." Lin M. Deola, Earthworks attorney said, "Insiders in the company traded on that information and then made a profit as a result of that."

Joe Groia, the former head of Enforcement for the Ontario Securities Commission, the Canadian equivalent of the SEC in the United States, said the rise in volume seemed unusual.

"From very small amounts, 100,000 shares a day or less, to very large amounts, 700-800 thousand shares... Someone looking at that is going to say, what has caused that sudden interest in this company?" Groia said.

In one transaction, more than 1 million shares were purchased on June 20 by a company "insider" and the director of an offshore investment firm, records show.

If a government employee tipped investors off to the EPA's pending decisions, that person may have violated the law and should be investigated as well, Deola said.

An EPA spokesperson said the agency "did not provide advanced notice" to Northern Dynasty or any of its investors "regarding either the timing or contents" of the decision on Pebble Mine.

The EPA says its top lawyer met with Pebble officials in advance, but also met with tribes and environmental groups opposed to the mine, which it says is a common part of the EPA's decision-making process.

In its SEC complaint, Earthworks also pointed to online posts on a stock tip website during an investor's conference on June 19 that Northern Dynasty CEO Thiessen attended, a week before the EPA announcement.

One post stated: "had a half-hour conversation with Ron [Thiessen] this morning" and later stated "if you are thinking about selling, don't."

The posts were removed shortly after CNN began asking questions. Northern Dynasty has denied that its CEO released any inside information.

Jacob Frenkel, a former SEC investigator, said the posts raise red flags.

"When you start to talk about an imminent announcement and the suggestion that information about an impending announcement is going to be positive for the company... the first thing I'm thinking about is, is there trading that takes place in advance of that announcement?" Frenkel said.

CNN has also obtained EPA notes documenting a June 26 agency meeting which was attended by scientific research teams and groups opposed to the mine. The EPA notes contained an allegation from organizations at the meeting that company officials had been speaking with investors.

"After the presentation," the EPA notes state, "the organizations noted that for the past several weeks, Northern Dynasty Minerals and the Pebble Limited Partnership have been telling investors that the EPA would be announcing a decision soon that would be very favorable to NDM and PLP."

Sean Magee, an executive vice president and spokesman for Northern Dynasty, denied that any company official traded on insider information.

"The insinuations you are making in your questions below are entirely false and without merit," he wrote in a statement to CNN.

Magee said the company's CEO did not tell investors in public or private conversations that he expected favorable decisions from the EPA. The CEO did, however, confirm he agreed with what the company called a "widely-held belief" that a decision on the project was imminent, Magee said.

Just days after CNN contacted the company, the online posts related to the CEO's comments were removed from the stock tip website. CNN was unable to identify or contact the author of the posts.

The security exchange experts interviewed by CNN said they believed the posts were problematic and questioned the timing of subsequent removal.

"It's absolutely relevant," Frenkel said. "Anytime potential evidence or information disappears from the marketplace, it creates additional suspicion."