Updated

Massachusetts Sen. Scott Brown says he won't cow to pressure from former Rep. Patrick Kennedy, whose father, the late Sen. Edward Kennedy, is being featured in a radio ad rejecting the mandate requiring religious employers to provide birth control coverage.

Kennedy asked the Republican senator to pull the ad claiming his father supported religious exemptions for employers and health insurers, but only on certain medical procedures, and not as a blanket exemption to deny birth control to employees.

"Providing health care to every American was the work of my father's life. The Blunt amendment you are supporting is an attack on that cause," the former congressman wrote, referring to the "conscience" exemption offered by Sen. Roy Blunt, R-Mo., in legislation facing the Senate.

"My father would never have supported this extreme legislation," reads the letter obtained by The Wall Street Journal.

Kennedy said he appreciates Brown's previous expressions of respect for his dad, who was known as the "Lion of the Senate," but "do not confuse my father's positions with your own .... misstating his positions is no way to honor his life's work."

Brown, who's in a tough reelection battle against Democratic challenger Elizabeth Warren, told reporters on Monday that he wouldn't take down the ad.

He added that he was "confused" by Kennedy's letter because the Rhode Island Democrat appeared to share the same position as his father on the issue and co-sponsored a similar conscience exemption bill when he was in Congress.

In a letter to Kennedy, Brown wrote that he believed his father "did not mean to put himself on the opposite side of the church or to suggest that he would force them to accept a situation with which they could not abide."

But the WSJ reports, Brown wrote that's exactly what the mandate forces religious groups to do.

"I'd like to think your dad would have been working with me to find an accommodation that all sides found satisfactory," reads the letter.