The Pofalla case, they said, was the latest demonstration of a faster-revolving door between the two sectors, and of the growing potential for business and political leaders to trade influence. Lobbying, while less intense here than in Washington or Brussels, still casts a large shadow, watchdog groups warned.

“For us, this is a clear signal that we quite urgently need a cooling-off period,” said Timo Lange, a spokesman for LobbyControl, an organization financed by small private donations that has been working since 2006 for regulation of lobbying. Those leaving the top ranks of government should wait three years before being able to lobby, he said, and lobbyists should be registered, as in the United States.

Almost worse than the speed of the transition in the Pofalla case, said Christian Homburg, the executive director of the German office of Transparency International, the anticorruption group, was that it appeared to revive an old tradition of creating lucrative jobs for long-serving politicians. His group endorsed a three-year pause.

On Friday, Mr. Pofalla, who has been a conservative member of Parliament since 1990 and retains his seat, declined to comment through his office, which said he would not be at work until the end of next week. Deutsche Bahn also had no comment. The deputy spokesman for Ms. Merkel’s government, Georg Streiter, told reporters that since Mr. Pofalla had left the government, there was nothing to say.

The reputation of Ms. Merkel’s government for staying out of business was called into question two months ago when a state minister in her chancellery, Eckart von Klaeden, 48, quit to join the Daimler auto company as chief lobbyist. The move had been mooted months earlier, fueling criticism that Mr. von Klaeden stayed on in government to influence successful lobbying by the German government in Brussels for less stringent emission limits on high-end cars.