Interest groups raising big donations to spend in this year's elections could face tough new limits under a proposal federal officials will begin considering this week.

The Federal Election Commission (search) is weighing how a new campaign finance law affects non-party groups that raise corporate, union and unlimited "soft money" donations and are active at election time.

Several commissioners call it the most important decision they will make this year.

The FEC is considering a wide range of options, from placing broad limits on soft money groups to sticking to the status quo and waiting to see what the groups do as the fall elections near. On Thursday, it is expected to start circulating a proposal for public comment. A final decision is expected in May.

The new law bars national party committees and congressional and presidential candidates from raising soft money, and it broadly restricts the use of big checks by others in federal elections.

Campaign finance watchdog groups contend both major parties are trying to get around the soft-money ban by using new non-party organizations run by party activists to collect the big checks and use them on get-out-the-vote drives, ads and other election-time activities.

The FEC last month decided to place some restrictions on outside groups' use of soft money. That decision covered only organizations that register with the FEC as political committees, declaring by doing so that one of their major purposes is spending money for or against federal candidates.

A draft proposal by commission attorneys released Monday suggests that the FEC consider whether it should broaden the range of groups considered political committees subject to its oversight and spending restrictions, perhaps sweeping in soft-money groups that do not currently register with the commission but are active in elections.

Other issues include what mix of soft and hard money should be required when groups are allowed to pay for activities using both, and whether any new rules should be delayed from taking effect until after the November elections.