House staffers could now miss their opportunity to get paid twice a month after a House bill to make the switch was muddied by a Senate amendment designed to tweak the ethics rules.

The House easily passed a bill allowing the change from monthly to biweekly paychecks two months ago. Senate staffers already are paid every other week.

But when the bill hit the Senate, Majority Leader Harry Reid (D-Nev.) and Minority Leader Mitch McConnell (R-Ky.) added an amendment changing a provision in the ethics rules passed last year.

Now the bill is in a state of uncertainty, with House leadership researching the effects of the change and assessing whether both sides of the aisle are on board.

“We are closely reviewing the Senate amendment to the legislation and following that careful review, we will announce our intentions on the bill,” said Nadeam Elshami, spokesman for Speaker Nancy Pelosi (D-Calif.).

Both Democratic and Republican staffers say the Senate amendment corrects an unintended consequence of the ethics law. Essentially, several junior Senate staffers are now covered by the lobbying ban — which prohibits former staffers from lobbying the Senate for one year after they leave — because their Christmas bonuses pushed them over the salary threshold.

Under the new law, staffers who make more than 75 percent of a Member’s basic rate of pay for “at least 60 days” fall under the lobby ban.

The issue threatens the long-awaited switch to biweekly paychecks in the House, where staffers have long relieved only one paycheck a month. Getting paid that infrequently makes budgeting difficult, especially for younger staffers on skimpy salaries.

About 54 percent of House employees are under 35. Seven percent of all House staffers earned $20,000 to $29,999 in 2007, while 21 percent earned $30,000 to $39,999.

The House bill gives the House Administration Committee the authority to change the pay schedule, and House officials have indicated that they would like to do so.

In April, the bill seemed well on its way. It passed the House just two weeks after it came out of committee; it was expected to quickly pass the Senate as well.

When House Administration Chairman Robert Brady (D-Pa.) first introduced the bill, Chief Administrative Officer Dan Beard heralded the change as “historic.”

“I think it’s an extremely important piece of legislation, and I’m thrilled that Mr. Brady has introduced it,” he said at the time. “It’s going to mean an historic change for House staff.”

But the Senate’s amendment, while a relatively simple fix for an unintended problem, involves a change to the ethics bill, which by its nature is controversial, and whose every nuance is carefully monitored. And that is enough to threaten — or at least delay— the House bill’s once all-but-certain passage.

Reid and McConnell’s amendment would change the timing for a lobby ban from “at least 60 days” to “more than two months.” The distinction is crucial to prevent Senate staffers who receive bonuses from being inadvertently caught up by the lobby ban.

“At least 60 days” covers four Senate pay periods. But because Senators are not allowed to give separate bonuses to their staff, many lawmakers temporarily inflate a staffer’s salary for four pay periods, or “at least 60 days.”

“More than two months,” however, would allow four bonus paychecks without reaching the new threshold.

Bonuses usually are awarded over four pay periods because staffers are not allowed to earn more than a Member.

For example, a staffer who makes $90,000 a year doesn’t meet the salary requirement for the ban, which is currently $123,900. But if that staffer got a $6,000 bonus over two months, his basic rate of pay would suddenly soar, and calculated over the entire year, would balloon to more than the threshold.

It appears that both Democrats and Republicans in the House eventually may agree to the change; a spokesman for Minority Leader John Boehner (R-Ohio) said there had been staff-level discussions and “no objections.”