Both groups said Bonta's subpoenas amount to an attempt to intimidate them and companies in the industry by chilling their free speech rights and advocacy before government agencies.
But California Deputy Attorney General Elizabeth Rumsey questioned claims from companies and the associations that they were being intimidated.
"We're talking about some of the biggest companies in the world," she said. "They express fear that they will be a target for legal threats, negative messaging and counter-advocacy efforts.
"I would translate that to a fear of being held legally accountable for any wrongdoing, and a fear of being called to stand behind their own speech in the public sphere," Rumsey said.
Mehta indicated he may be undecided on that point.
"That's one way of looking at it," Mehta said to Rumsey. "Another way of looking at it is they have associational rights just as you and I do, and they don't want to have their communications they otherwise cloaked in associational rights, spill out into the public.
"Because certainly the attorney general hasn't given them any assurance that he won't do that," the judge said. "I don't think it's as simple as you suggested."
Mehta did not make a ruling and gave all three parties until the end of the week to submit additional information on relevant case law to the court.
He likely needs to rule before two California state courts hold hearings in mid-September on enforcing the subpoenas.
Besides substantive claims, the hearing to grant a preliminary injunction blocking subpoena enforcement delved into issues of standing in the federal courts and how the parties have served their filings on the other side.
Bonta has subpoenaed others, including ExxonMobil Chemical Co., as part of his investigation. Inside Climate News reported Aug. 24 that Bonta said the investigation is nearing completion.
Mehta also asked the plastics association to provide him with a copy of the contract that the association had with the Hagley Library and Museum in Delaware to store its archives there.
Beginning in 1988, the association kept records dating back to at least the 1970s in Hagley's archives.
Bonta has sought access to those records, but the association has argued that access is limited to scholars and that information can only be quoted "extensively" with the association's permission. It also said access for litigation is limited.
The PBS news show Frontline, however, said it used documents from the Hagley Library in its Plastic Wars 2020 documentary with National Public Radio.
Bonta cited that documentary in a news release announcing his investigation in 2022, saying it revealed internal industry documents from the 1970s showing that executives had serious doubts that recycling would be economically feasible.
Previously, the plastics association had disclosed to the court it was in the process of removing the records from Hagley. Michael Kirk, an attorney with Cooper & Kirk LLC representing the plastics association, told Mehta during the hearing that the records have been moved.
"Since the papers were filed, your honor, I think we had indicated that we were taking steps to retrieve them," Kirk said. "I did want to tell the court that's been concluded. They are no longer at Hagley."
Kirk also said the association could provide the court with anonymous declarations of member companies that the subpoena was chilling their ability to participate in government advocacy with the association.