For the second time in recent months, the corporate owners of the Great America theme park have sent a warning shot to the city of Santa Clara, suggesting they will oppose or sue over the proposed $937 million stadium for the 49ers if they don't get more promises and concessions as part of the deal.

In a Sept. 3 letter to the city from Cedar Fair Entertainment's lawyer, the park owners say they have not been properly insulated against the potential loss of business if the stadium is built, even if the team follows through with its assurance it will compensate Great America for lost profits if it closes on game days.

In addition, the letter accuses city officials of failing to disclose the potential additional cost to taxpayers if Great America suffers greater-than-expected financial losses connected to the stadium. Great America leases its property from Santa Clara, providing the city about $5 million in revenue each year.

"Cedar Fair does not believe that the proposed stadium and Great America can coexist without overcoming significant legal and operational issues," attorney Geoffrey Etnire wrote to Santa Clara City Manager Jennifer Sparacino. "However, Cedar Fair will come to the table in good faith to explore possible resolution of this conflict."

In another development Thursday, the state Senate approved a bill that would allow Santa Clara to avoid a public bidding process on a portion of the proposed stadium. The bill, backed by Sen. Elaine Alquist, D-San Jose, would allow the team to select its general contractor to design and build the stadium without public bidding, but would still require competitive bidding on any public dollars spent on the stadium. The governor has 30 days to sign the bill.

Meanwhile, the latest in Cedar Fair's back-and-forth public posturing over the proposed stadium comes as the city is nearing a crucial point in pushing the deal toward a ballot measure. The deadline for public comment on the draft environmental impact report released this summer on the stadium is scheduled for Monday, which would set the stage for public hearings in October.

Santa Clara voters are expected some time next year to decide whether to approve up to $114 million in redevelopment financing and hotel tax revenue for the stadium project, which would be built on Great America parking lots for the 2014 NFL season.

City officials and 49ers representatives downplayed the most recent letter from Cedar Fair, which comes after another missive in July warning the city it wants more information on the impact of the stadium. Cedar Fair officials have expressed various opinions on the stadium proposal over the past two years, ranging from outright opposition to support, as well as indicating the company might be willing to sell the park to the team.

Assistant City Manager Ronald Garratt said the city has consistently looked to make sure Great America's interests are protected, and that any uses of the stadium fit with the park's interests.

"It is absolutely the city's intention to protect Cedar Fair's business, to protect the income they need to be in business," he said.

Lisa Lang, spokeswoman for the 49ers, said the team had no comment on the letter, adding that it was a matter between the city and Cedar Fair. However, Lang expressed frustration with the fact that the park owners appeared more interested in sending threats than negotiating.

"Unfortunately, they have declined to participate every step of the way," Lang said. "The team is mystified why Cedar Fair's attorney would choose to send a letter like this instead of pulling up a seat at the table."

Duff Milkie, Cedar Fair's general counsel, said the company has reached a point where it has to "protect its interests" because the city and 49ers have not given the park owners any specifics.

"We've yet to see anything concrete," he said. "So we're laying out our concerns, here they are."

In the letter, Cedar Fair officials focus on concerns that the construction of the stadium and shutdowns on game days could deteriorate Great America's business beyond what the team has offered to offset any lost profits, and cut off chances to expand. The letter expresses particular concern if the stadium ultimately houses the Oakland Raiders as well as the 49ers, which has been raised as a possibility and would double the number of game days.

In addition, the letter says the city and team have been proceeding with the stadium proposal despite what Cedar Fair considers unanswered legal questions about the right to build the stadium on Great America's parking lots. The letter raises the prospect of a lawsuit, arguing that building the stadium could violate the terms of the park's lease with the city.

Garratt disputed that argument, saying the lease has always envisioned development of the parking lot property.

Contact Howard Mintz at 408-286-0236