The phrase "a letter asserting that" is correct and usable in written English.
You can use it when referring to a letter that makes a claim or statement about something.
Example: "I received a letter asserting that my application had been approved."
Alternatives: "a letter claiming that" or "a letter stating that".
It fired off a letter asserting that district official misunderstood the court ruling.
The law, 3 U.S. Code section 15, allows for a challenge to electoral votes — either on an individual basis or statewide — if one member of the House and one member of the Senate submit a letter asserting that votes were not "regularly given".
A Howard University trustee acknowledged Saturday that she had written a letter asserting that the school "is in genuine trouble" for various fiscal and management reasons, but she declined to elaborate.
On Sept. 14, one day after the Fox News story, the Shurat HaDin Israel Law Center sent Bollinger a letter asserting that because the U.S. State Department lists Iran as a state sponsor of terrorism, "hosting Ahmadinejad is not merely morally repulsive: it is illegal and will expose Columbia University and its officers to both criminal prosecution and civil Liability".
But in some ways Mr. Ban's commemoration remarks at the United Nations headquarters, on a day it has designated World Humanitarian Day, were overshadowed by aggrieved staff members, whose union representative presented Mr. Ban's office with a letter asserting that his internal labor policies had compromised their safety and security.
Mr. Kasparov was taken into custody during a scuffle between protesters and security officers on the route to the offices, where he had intended to present a letter asserting that the parliamentary election on Dec. 2 was biased toward President Vladimir V. Putin's party.
They were answered by Mr. Fitzpatrick, who, in a letter, asserted that ABC did, indeed, test produce for pesticide residue.
(A museum? Inside a museum?) Dubbed the "L.A. Emale Action," the Guerilla Girls' letter asserts that, of the thirty artists in the show, ninety-seven per cent are white and eighty-seven percent are men.
The lawmakers' letter asserts that "it was clearly never, as administration officials once insisted, the result of a popular protest".
A gaggle of neoconservative analysts wrote an open letter asserting that "The Assad regime poses a grave threat to national security interests of the United States," but what interests are those?
Mr. Schrems said his group planned to send the Irish regulator a formal letter asserting that the regulator's audit of Facebook was unsatisfactory and allowed the company to operate in Europe without adhering to E.U. data protection law.
