WASHINGTON — Lawmakers take contributions every day from corporate executives and lobbyists hoping for their votes. The question of whether that represents business as usual in Washington or an ethics breach is at the heart of a far-reaching Congressional ethics investigation that is stirring concerns throughout Washington and Wall Street.

The Office of Congressional Ethics has sent corporate donors and fund-raising hosts more than three dozen requests for documents involving eight members who solicited and took large contributions from financial institutions even as they were debating the landmark regulatory bill, according to lawyers involved in the inquiry.

The requests are focusing on a series of fund-raisers last December, in the days immediately before the House’s initial adoption of the sweeping overhaul, which could win final approval this week. Some of the fund-raising events took place the same days as crucial votes.

For example, on Dec. 10, one of the lawmakers under investigation, Representative Joseph Crowley, a New York Democrat who sits on the Ways and Means Committee, left the Capitol during the House debate to attend a fund-raising event for him hosted by a lobbyist at her nearby Capitol Hill town house that featured financial firms, along with other donors. After collecting thousands of dollars in checks, Mr. Crowley returned to the floor of the House just in time to vote against a series of amendments that would have imposed tougher restrictions on Wall Street.