City Attorney Jan Goldsmith says there are an array of legal problems and significant risks to taxpayers in The Citizens Plan, an initiative that would hike San Diego hotel taxes and possibly fund a convention center annex.

Goldsmith, who issued a 25-page memo on the initiative Monday afternoon, said those concerns could prompt him to recommend the City Council not place the measure on the ballot or consider filing suit to block it.

If the measure doesn’t make the November ballot, it could be good news for a separate citizens’ initiative seeking to raise local hotel taxes to fund a joint Chargers stadium/convention center annex.

Some have raised concerns that having two similar measures on the ballot could confuse voters, or that conflicts between the two measures could create problems if voters approve both in November.

Attorney Cory Briggs, principal author of the Citizens’ Plan, said in a brief response on Monday that his coalition isn’t worried about the issues Goldsmith is raising and that the city attorney is wrong about every one of them.

Briggs also said his group had "another productive meeting" on Monday with the Chargers about how the two conflicting measures deal with the future of Mission Valley, but he declined to provide further details.

Meanwhile, on Tuesday Briggs plans to hold a news conference to announce a settlement with the San Diego Tourism Marketing District over a lawsuit he brought on behalf of his client, San Diegans for Open Government, challenging a tax on hotel guests to fund marketing. He also said on Twitter that he plans to comment on the timing of the city attorney's opinion.

Mayor Kevin Faulconer , who requested the legal analysis from Goldsmith, said the memo made him especially concerned about potential litigation.

"While there are some well-intentioned ideas in this proposal, the city attorney's analysis shows that this appears to be a plan that could tie up the city in court for years at great cost to taxpayers," Faulconer said Monday.

In his memo, Goldsmith describes in detail six separate problems with the wide-ranging measure, including that it would give hoteliers improper control of city tax money and that it would violate state initiative law by addressing more than one central issue.

The measure, unveiled in October, would also improperly trump the authority of the San Diego Unified Port District by dictating how the organization would spend money, Goldsmith said.

In addition, it would replace existing state environmental law with local statutes that Goldsmith says go "well beyond current law, including recent Supreme Court decisions."

The measure’s local environmental approval process would also increase the city’s litigation risks, Goldsmith said, by widening who could sue the city on environmental grounds and eliminating time limits for the filing of litigation.

The greatest risk to taxpayers, however, would be the initiative’s so-called "poison pill" provision that says the entire measure is null if any one element of it is deemed illegal, Goldsmith said.

That could make it dangerous to collect and spend revenue generated by the initiative, which would increase the city’s hotel tax from 12.5 percent to 15.5 percent, because that money would have to be returned if litigation nullifies any part of the measure.

Such risk could make it difficult or impossible to sell bonds for convention center construction that would be repaid by the additional hotel tax revenue, Goldsmith said.

"There's nothing illegal about it, but it says 'you find one flaw in this thing then it's all invalid,’" he said. "At any time in the future, there could be claims raised. Then what do you about all those illegally collected taxes if this whole thing goes away?"

If the Briggs coalition gathers enough signatures to place the measure on the ballot, Goldsmith said the concerns could prompt him to recommend the council decline to do so.

In addition, he said the city could sue to block the initiative, something San Diego previously did successfully on a citizens’ initiative related to construction of Petco Park.

Such a suit could be filed before the election or afterward, he said.

"There's also the potential the proponents would not submit it," Goldsmith said. "There are a lot of different options."

Because supporters have already begun gathering signatures, they couldn’t make any changes now without starting the entire process over, Goldsmith said.

Among the legal problems is the measure’s stipulation that hotel owners could divert part of the additional hotel taxes into a special infrastructure fund for a convention center expansion.

Goldsmith said this violates the city charter, which requires all tax money to be collected by the city treasurer and prohibits the City Council from delegating its control over tax revenues.

By addressing multiple subjects simultaneously, the measure would also violate the "single subject" requirement of state initiative law, which forces citizen groups to focus on one goal, Goldsmith said.

The measure would only raise one kind of tax, but it goes beyond one issue by creating incentives and requirements related to use of the former Qualcomm Stadium site, prohibition of waterfront convention center expansion and the city’s environmental requirements.

"It’s got a lot of different elements in there and I don’t know how you tie them together," he said. "It’s designed to bring a large coalition together, but that’s exactly what the single-subject rule is there to protect against."

Supporters of the initiative, a group that includes development firm JMI and former Councilwoman Donna Frye, have said the unifying theme of the measure is responsible management of tourism-related facilities.

The measure would require developers of projects in an overlay zone near Petco Park to pay mitigation fees of $15 million to the Port District and $5 million to help upgrade the Qualcomm site, where there would be university-related facilities and parkland along the San Diego River.

It would also require the Port District to combine that money with $35 million in additional funds for projects on the embarcadero.

Goldsmith said that would illegally usurp the authority of the Port over its finances, noting that the Port represents Chula Vista, National City, Imperial Beach and Coronado, not just San Diego.

The city attorney was particularly critical of the Citizens’ Plan on environmental approvals, which supporters have said would be easier than under state law.

While it would allow developers in an overlay zone near Petco Park to bypass the state’s rigorous environmental laws, it would replace them with new local rules that Goldsmith called arguably tougher.

The city would also be more vulnerable to litigation, he said. That’s because state law limits lawsuits to people and groups who were involved in the city’s environmental analysis, but the Citizens’ Plan would not.

In addition, state law says lawsuits must be filed within 30 days of certification of an environmental impact report, but the measure creates no such time limit.

Goldsmith also questioned whether the measure expands too liberally a 2014 Supreme Court decision allowing projects proposed by citizen’s initiative to bypass state environmental law.

He said that ruling appears to apply only to individual projects, such as the Rams new stadium in Inglewood, not an entire district where multiple projects could be proposed over many years.

"We think this is stretching the law," Goldsmith said. "It’s certainly testing the boundaries of the law."

Goldsmith’s memo says it’s unclear whether the measure would need approval from two-thirds of voters or a simple majority, because a March 18 appellate court ruling appears to indicate citizen’s initiatives only require simple majority approval.

Without that case, which the Supreme Court could endorse or overturn this summer, Goldsmith said the measure would require two-thirds approval because it raises taxes for a specific purpose: construction of a convention center annex.

Supporters of the Citizens’ Plan have argued, even before the March appellate ruling, that it would need only simple-majority approval because the increase in hotel taxes would be for general purposes.