A bipartisan coalition of advocacy and legal groups is preparing litigation to force the Massachusetts Legislature to comply with a voter-approved legislative audit law if Beacon Hill pols refuse to participate come the new year willingly.

The threat of a lawsuit comes as Auditor Diana DiZoglio has already asked Attorney General Andrea Campbell to greenlight legal action that would force the House and Senate to hand over internal information as part of a renewed effort to investigate the two chambers.

Leaders of the coalition — which includes the Massachusetts Fiscal Alliance, Act on Mass, and the Pioneer Institute — said they are preparing their own court challenge for January in the event Campbell does not approve DiZoglio’s legal request and the Legislature continues to stonewall an audit.

Frank Bailey, a retired federal judge and head of the Pioneer Public Interest Law Center, said his organization is ready to take the lead on the potential lawsuit, which would likely be filed in state Superior Court with the aim to end up before the Massachusetts Supreme Judicial Court.

“We think that government officials should follow the law, and it’s our intention to make sure that in this instance, if they don’t do it voluntarily, which we hope they do, then we stand ready at Pioneer Law Center to initiate such litigation as might be necessary in order to achieve that result,” he told reporters while standing in front of the House Chamber.

The successful ballot question granting the State Auditor’s Office the right to crack open the books of the Legislature has found itself on a contentious path even before residents approved it with 72% of the vote in November.

Senate President Karen Spilka and House Speaker Ron Mariano have long argued that an audit violates the separation of powers outlined in the state constitution. The two leaders have so far spurned DiZoglio’s attempts to engage in a probe.

Lawyers for the branches and Secretary of State William Galvin’s Office have also tussled with DiZoglio over the implementation date of the new law — 30 days after the Nov. 5 election or 30 days after election results are certified.

Spilka and Mariano have also left the door open to tinkering with the audit law next year, a scenario that has enraged supporters of the measure.

Spokespeople for the two lawmakers did not immediately respond to a request for comment.

DiZoglio sent a letter on Dec. 5, the date she argued the law took effect, to legislative leaders informing them of an investigation into the two chambers that was set to focus on finances, state contracts and procurement, nondisclosure agreements, and other internal proceedings.

It was one of multiple missives DiZoglio has transmitted to the House and Senate detailing a forthcoming audit. Lawyers for the House and Senate have declined to participate in each of the first two instances.

In a letter sent to DiZoglio in November, in-house attorneys for the Legislature said the auditor still lacked the legal authority to probe the two chambers because the law does not take effect until Jan. 3, or 30 days after election results are certified.

“Your request is untimely,” the lawyers said.

Massachusetts Fiscal Alliance spokesman Paul Craney said the lawsuit, which will include a “robust” finalized plaintiff list, may not be necessary if one of two things happen — either Mariano and Spilka agree to an audit or Campbell takes “up this good government issue and force(s) the implementation of the ballot question.”

Craney described the situation as a “political gift” to Campbell that the former Boston city councilor could capitalize on.

“The biggest winner could potentially be the attorney general, who could take up this worthy cause, and our potential lawsuit would not be necessary,” he said. “If this gift to the attorney general is not realized, and if legislative leaders continue to deny the results of the election, we will be here in January, we will file a lawsuit.”

A spokesperson for Campbell did not immediately respond to a Herald inquiry.

In a statement to the Herald, DiZoglio said she was “saddened by the attorney general’s continued unwillingness to intervene and help.”

The coalition attempting to force the House and Senate to comply with the law is an unlikely group.

The Massachusetts Fiscal Alliance, a conservative organization, has banded up with Act on Mass, a progressive group focused on government transparency, the Pioneer Institute, and officials with the Massachusetts Republican Party.

Scotia Hill, the executive director of Act on Mass, said lawmakers on Beacon Hill should not “waste time and precious political capital fighting an initiative on which voters have already plainly spoken.”

“It shouldn’t have to come to this that citizens would be so unconfident, so uncertain, that our legislators are operating in their best interest, that they would be forced to resort to the ballot to ensure that it is properly investigated,” Hille said.