The complaint, filed in Washington federal court Tuesday said the Maritime Administration, a branch of the Department of Transportation, had effectively delayed the loan guarantee decision for the past two years. The company is demanding the court direct the agency, which oversees the loan program, to make a decision before an Aug. 31 deadline.

If APT's application is not approved or denied before Aug. 31, the company said it would be forced to reapply. Were that to happen, other companies in line for loans would move ahead of APT. APT alleged that there is not enough money for everyone.

A source close to the situation said approval or denial is expected before the Aug. 31 deadline. Cerberus Partners LP also owns a stake.

The complaint also requests that the court prevent Secretary of Transportation Ray LaHood from "further interference" with the Maritime Administration's ability to make a decision.

That gets to the heart of the issue as it relates to private equity: APT claims that LaHood told the Maritime Administration to get a recommendation about whether to approve the loan from the Department of Transportation Credit Council -- which APT said was outside the scope of his statutory authority. The Credit Council oversees four loan programs including the loan APT was applying for, the Maritime Guaranteed Loan (Title XI) Program, which can be used to finance or refinance the construction of shipping vessels.

The problem for APT is that the Credit Council allegedly had concerns about the company's private equity backers.

"I've asked the Maritime administrator on numerous occasions what do we have to do. He said, 'I don't know,' " APT chief executive Robert Kurz said in an interview. "He's told me numerous times that it has to do with our ownership."

The company said that after it filed its application for $470 million of Title XI loan guarantees in the summer of 2010, in hopes of refinancing the cost of constructing five 49,000-deadweight-ton petroleum tankers it built between 2006 and 2010, it had a brief back-and-forth with the Maritime Administration. After a March 2011 meeting, the Maritime Administration "advised APT that the Credit Council had denied the request and had, in addition to expressing a funding concern, now raised an issue about whether Title XI financing should be made available to shipping companies owned by private equity firms such as Blackstone."

The refinancing is important to the company because it wants to replace a $256 million, five-year loan it is paying about 10.25% on at an interest rate closer to 3% to 3.5%.

Private equity has been central to the ongoing presidential race, with former private equity executive Mitt Romney as the presumed Republican candidate. The industry has been a target of attack ads from the Obama campaign.

APT, of course, said that who owns the company should not matter. Blackstone declined to comment beyond the complaint. The Department of Transportation said that APT's application is under review and declined to comment on the litigation.

In the complaint, APT said it eventually met with John D. Porcari, the Transportation Department's deputy secretary, in late 2011, and alleged that it had "resolved the Deputy Secretary's concerns about APT's ownership."

To ensure that the application was sound, APT alleged that it proposed to reduce the loan amount from $470 million to $400 million, while also reducing the guarantee period by 3-1/2 years to 20 years.

More delays came, APT said in its lawsuit. One reason given, the company said, was that there is additional scrutiny in place for loan programs after solar manufacturer Solyndra Corp. filed for Chapter 11 bankruptcy in 2011, from the default on its $535 million Energy Department loan.

To make its application more attractive, the complaint said, APT lowered the amount it was asking for to $340 million. The company said in the complaint that $340 million is worth only 51.2% of the cost of its tankers, much lower than the 87.5% of the actual cost it could apply for. Regulations allow a 2-to-1 debt-to-equity ratio, the complaint said, while APT's will only be 0.88-to-1.