A group of 13 lawmakers tabled a letter asking if financing for the property had been mentioned in talks between Mr Kushner and foreign delegates.
Kushner Companies owns at least half of 666 Fifth Avenue in Manhattan, which in the decade since its purchase has proved a significant financial drain.
The underoccupied tower will bring expected $24m (£18m) this year, and the debt on the property is due in two years.
Mr Kushner was head of Kushner Companies until he sold the interest to a family trust earlier this year.
Before he joined the administration, he sought help from foreign investors over the troublesome tower block, meeting with South Korean and Chinese executives to discuss buy-ins.
According to Bloomberg, the company hopes to replace the 1950s office block with luxury flats, a hotel and a large shopping mall – but the grand aspirations have floundered after limited support from its partners.
Now an adviser to President Trump, Mr Kushner is being questioned over possible collusion between Russia and Trump’s successful 2016 presidential campaign.
It is not known whether the debt on the property at number 666 is being investigated by the inquiry.
In the letter to Mr Kushner, lawmakers said they were “concerned” that he may be leveraging his “White House position to seek financial assistance” for the property.
They asked whether he had discussed help for finance, purchase or debt assistance to the building with any foreign nationals or entities since the election of his father-in-law in November 2016.
Saudi Arabia, China, Israel and France were suggested as countries of interest.
Enquiries into Mr Kushner have so far found he was present at a back-room meeting with Natalia Veselnitskaya, a Russian lawyer, which Donald Trump Jr had organised in the hope of uncovering information that might be damaging to Hillary Clinton.
This week, US media named Mr Kushner as the White House official who had directed Michael Flynn to reach out to Russia as part of an attempt to delay a UN resolution on Israeli settlements.
A White House spokesperson declined to comment on the issue and Mr Kushner’s lawyer, Abbe Lowell, could not be reached for comment.
Mr Trump has denied any collusion between the Kremlin and his presidential campaign.
The lawmakers asked Mr Kushner to respond by 12 December.