Credit Union asking for W-8BEN for loan when I'm a Resident Alien for Tax Purposes. Should I fill W9 instead? Am I committing perjury if I'm forced to fill possibly wrong form?

If you have met the Substantial Presence Test under under hour H1-B visa, and have filed a Form 1040 tax return, provide the credit union with a copy of your tax return.  That Form 1040 tax return can only be filed by a U.S. citizen or resident alien.

According to the IRS Instructions for Form W-8BEN at this link:

Do not use Form W-8BEN if you are described below.

• You are a foreign entity documenting your foreign status, documenting your chapter 4 status, or claiming treaty benefits. Instead, use Form W-8BEN-E.

• You are a U.S. citizen (even if you reside outside the United States) or other U.S. person (including a resident alien individual). Instead, use Form W-9 to document your status as a U.S. person.

• You are acting as a foreign intermediary (that is, acting not for your own account, but for the account of others as an agent, nominee, or custodian). Instead, provide Form W-8IMY.

• You are a nonresident alien individual who claims exemption from withholding on compensation for independent or dependent personal services performed in the United States. Instead, provide Form 8233 or Form W-4.

• You are receiving income that is effectively connected with the conduct of a trade or business in the United States, unless it is allocable to you through a partnership. Instead, provide Form W-8ECI. If any of the income for which you have provided a Form W-8BEN becomes effectively connected, this is a change in circumstances and Form W-8BEN is no longer valid with respect to such income. You must file Form W-8ECI. See Change in circumstances, later.