Washington, D.C. ? Tom Loeffler, the national finance co-chairman for Sen. John McCain’s presidential campaign, resigned Sunday because of his lobbying ties, a campaign adviser said.

He is the fifth person to sever ties with the campaign amid a growing concern over whether lobbyists have too great an influence over the Republican nominee. Last week, campaign manager Rick Davis issued a new policy that requires all campaign personnel to either resign or sever ties with lobbying firms or outside political groups.

McCain has built his reputation in Congress on fighting special interests and the lobbying culture, but he has been criticized for months about the number of lobbyists serving in key positions in his campaign. Until recently, his top political adviser, Charles R. Black Jr., was the head of a Washington lobbying firm. Black retired in March from BKSH & Associates, the firm he helped found, to stay with the campaign. Davis ran a lobbying firm for several years but has said he is on leave from it.