WASHINGTON — Scrutiny of drug and consumer product giant Johnson & Johnson ratcheted up Tuesday as a congressional chairman demanded the company provide proof of its claim that federal regulators cleared a plan to secretly buy up defective painkillers.

The letter from Rep. Edolphus “Ed” Towns, D-N.Y., comes a week ahead of a hearing to scrutinize J&J’s “phantom recall,” conducted last year, when the company paid an outside contractor to quietly purchase more than 88,000 packets of Motrin off store shelves.

A J&J executive testified in May that the FDA “was aware” of the action. And internal e-mails among J&J employees state that the company “negotiated an agreement with FDA not to formally conduct a recall.” The e-mails were released by the House Oversight and Government Reform Committee, which Towns chairs.

The FDA has stated that it did not know of J&J’s secret purchase plan until July 2009, when it demanded the company recall the product, which did not dissolve correctly.

Towns’ letter asks William Weldon, J&J’s chairman and chief executive officer, to provide a copy of the alleged agreement between his company and the FDA, or describe its terms if it wasn’t written down.

FDA Deputy Commissioner Joshua Sharfstein, an Obama appointee, is scheduled to appear at the committee’s hearing Sept. 30.

Congress’ investigation into J&J originally centered on a series of nine recalls of over-the-counter medications over the past year.

The recalls have involved problems ranging from liquid medicines that may contain tiny metal shavings and drugs that may not have the correct amount of active ingredient.