Three women have accused Gordon D. Sondland, the United States ambassador to the European Union, of making unwanted sexual advances toward them years before his recent turn as a star witness at the impeachment proceedings against President Trump, according to a news report.

The women shared their accounts with ProPublica and Portland Monthly, which published them online Wednesday in a joint investigative project between the nonprofit news organization and the Oregon magazine.

The publication of the allegations came exactly one week after Mr. Sondland appeared before Congress and gave what was widely viewed as damaging testimony about Mr. Trump’s dealings with Ukraine and a “quid pro quo.” Mr. Sondland, 62, a businessman and hotelier, contributed $1 million to Mr. Trump’s inaugural committee.

The report identified the three women as Jana Solis, Natalie Sept and Nicole Vogel , who is the owner of Portland Monthly. The magazine said that Ms. Vogel was not involved in editorial decisions and that the magazine’s editorial team decided independently to pursue the story.