WASHINGTON — Earl Pomeroy figured that Plan A was his career in Congress, where, over nearly two decades, as a North Dakota congressman he became a powerful advocate for the hospital industry.

Now, after losing re-election last year despite hundreds of thousands of dollars in campaign donations from grateful hospital executives, doctors and other industry officials, he has moved on to Plan B: promoting their cause as a lobbyist.

While that kind of shift is familiar in Washington, in Mr. Pomeroy’s case there is a special twist. House members are banned from lobbying on Capitol Hill for a year after leaving office (Mr. Pomeroy’s term ended in January), but Mr. Pomeroy, a Democrat, has teamed up with his former chief of staff, who is not subject to the restriction, as a lobbying partner.

Just as Mr. Pomeroy once pushed in Congress to expand federal health care programs and block regulatory proposals that industry executives considered burdensome, he and his former aide, Bob Siggins, now are pressing the Obama administration and Congress to drop a planned change in Medicare rules that could force dozens of long-term care hospitals to close or curtail services. Mr. Pomeroy’s clients, Select Medical Holdings and Vibra Healthcare, operate such facilities across the country.