US ATTORNEY ANDREW LELLING has sent a chilling response to calls from pro-pot advocates to clarify his stance on marijuana prosecution in Massachusetts, a message sure to send potential investors and business people into a state of panic over whether they would be subject to arrest and prosecution under federal drug laws.

“This is a straightforward rule of law issue,” Lelling said in a statement issued by his office Monday. “Congress has unambiguously made it a federal crime to cultivate, distribute and/or possess marijuana.  As a law enforcement officer in the Executive Branch, it is my sworn responsibility to enforce that law, guided by the Principles of Federal Prosecution.”

US Attorney Andrew Lelling

While Lelling went on to state he would decide on a “case-by-case basis” whether to prosecute marijuana-related crimes, his hard-line language will give many entrepreneurs pause before moving forward, said advocates.

“This presents a very ominous landscape just when the [Cannabis Control Commission] is forming regulations for the industry,” said James Borghesani, the communications director for the ballot question that legalized pot who issued the challenge for a “clear and unambiguous” stance from Lelling. “This is the last thing that Massachusetts needed. It is diametrically opposed to the will of the voters. I guess it doesn’t surprise me; it appalls me.”

Lelling’s statements comes in the wake of a change announced by Attorney General Jeff Sessions to scrap the hands-off approach by the former Obama administration that gave states a safety net to legalize marijuana without fear of federal prosecution. Under federal law, marijuana is classified as a Schedule 1 controlled substance, in the same category as heroin, making it illegal under federal law regardless of state laws. There are now eight states, including Massachusetts, that allow the legal sale of recreational marijuana.

Lelling had issued a statement last week that was unclear just what his approach would be so advocates over the weekend demanded that he clarify his approach. His new statement is in stark contrast with the interim US attorney in Colorado, who said he would not prosecute legal marijuana growers, sellers, or users.

“I understand that there are people and groups looking for additional guidance from this office about its approach to enforcing federal laws criminalizing marijuana cultivation and trafficking,” Lelling said in his statement. “I cannot, however, provide assurances that certain categories of participants in the state-level marijuana trade will be immune from federal prosecution.”

Gov. Charlie Baker, who last week criticized Sessions’ decision to overturn the Justice Department’s approach, reiterated his support to move forward with implementing the voter-approved law.

“Governor Baker will continue to support the [cannabis commission’s] mission and the administration will also continue to adequately fund the commission’s work as they develop regulations for the marijuana industry in Massachusetts,” Baker spokeswoman Lizzy Guyton said in a statement.

Acting Senate President Harriette Chandler, emerging from a leadership meeting with Baker and House Speaker Robert DeLeo, said Lelling’s statement will definitely have an impact on the nascent industry.

“There’s a great deal of uncertainty that surrounds this marijuana industry,” she said. “It obviously determines whether people can go into the industry with some level of certainty.”

DeLeo, who had been opposed to the referendum and has been tepid in support of the new industry, said he is unclear what Lelling meant by “case-by-case basis” in determining who to prosecute.

“I’m not exactly sure what that means, DeLeo told reporters. “I’m not sure what type of message that sends or what type of security that gives you or lack of security that gives you.”

A spokeswoman for Attorney General Maura Healey, who also opposed the ballot question, said Lelling’s stance still required further clarification.

“The people of Massachusetts voted to legalize the responsible sale and use of marijuana. Our office is committed to helping implement legalization effectively and as safely as possible,” Jillian Fennimore said in a email statement. “We encourage the U.S. Attorney to further clarify his enforcement priorities to provide guidance to Massachusetts municipalities, residents and businesses.”

Representatives from the state Cannabis Control Commission, which meets on Tuesday, did not immediately respond to a request for comment.