The Internal Revenue Service unit under fire for its reviews of conservative organizations has a long history of targeting groups with extra scrutiny, including foreclosure-assistance charities, credit-counseling services and New York Jewish charities, interviews with current and former employees show.

The scrutiny has included such tactics as listening to telephone calls between groups and their clients, according to one group’s lawyer. In the case of tea-party organizations, IRS officials studied social-media postings to gauge political activity.

Sometimes the tactic of extra scrutiny for particular kinds of groups seeking tax exemptions helped manage a flood of entities in areas where abuse was common; other times it snagged innocent parties, subjected applicants to long delays and even made IRS employees feel uncomfortable…

This picture of how the unit operates offers fodder for both sides in the current debate. IRS defenders say the agency has long resorted to clustering similar entities to make its scrutiny more efficient, and didn’t do so just in the case of conservative groups. “It makes sense to put cases together so you can see trends,” said Bonnie Esrig, a former longtime IRS manager who, before her January retirement, was assigned for 18 months to a Cincinnati unit that reviewed tax-exempt applications.