The watchdog organization Citizens for Responsibility and Ethics in Washington (CREW) is urging all 2020 presidential candidates to release their tax returns from at least the last 10 years, after President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE became the first major-party nominee in decades to refuse to disclose any filings.

“Tax returns can illuminate conflicts and can also shed important light on a president or candidate’s charitable giving and whether they are paying their fair share of taxes,” CREW Executive Director Noah Bookbinder said in a statement on Thursday.

CREW also launched a webpage to track which 2020 candidates have released tax returns. It allows viewers to download tax documents that have been released.

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So far, two Democratic candidates have released at least 10 years of tax returns: Sens. Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (Mass) and Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (N.Y.). CREW said some others have not released any tax returns to date, while others have shown only specific reporters some of their tax returns or have only released summaries of their documents in the past.

The group noted that Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) only released one year of his tax returns during his 2016 bid for the Democratic presidential nomination. After announcing his 2020 run last month, Sanders said he would release 10 years of tax returns.

CREW said on its website that providing at least 10 years of tax returns is "in the interest of transparency," and said that the types of limited disclosures that some candidates have made in the past "do not go far enough to shed light on possible conflicts, or to show the public a full picture of presidential candidates’ finances."

The launch of CREW's tracker comes as House Democrats plan to try to obtain Trump's tax returns by requesting them from the Treasury Department. Trump in 2016 broke with precedent and refused to make his tax returns public, citing an IRS audit. However, the IRS has said that audits don't prevent people from making their own tax information public.

Democrats have expressed interest in viewing Trump's tax returns to learn more about any potential conflicts of interest involving foreign governments, and to see how the president may have benefited from his 2017 tax-cut law.

The House earlier this month passed legislation that would require presidents, vice presidents and major-party nominees for those offices to disclose 10 years of personal and business tax returns. Bookbinder testified at a hearing in February in support of the legislation.