When federal immigration agents raided a Houston rag factory and took 166 suspected illegal immigrants into custody, a Boston philanthropist and multimillionaire was ready to chip in bond money to help the workers.

Robert J. Hildreth, 57, is the public face of the National Immigrant Bond Fund, a fledgling organization that helps immigrants swept up in Immigration and Customs Enforcement workplace raids post bonds.

The controversial fund has the backing of major immigrant advocacy groups and religious leaders, but has drawn criticism from anti-illegal immigration organizations.

Since spring 2007, the fund has paid more than $180,000 to bond out immigrants snared in ICE raids in California, Massachusetts and Maryland.

Word of the fund is spreading, but not quite fast enough for some immigrants caught up in the recent crackdown on businesses that hire illegal immigrants. In the past nine months, ICE has detained about 4,500 undocumented workers and 111 employers, according to ICE statistics. ....