WASHINGTON (Reuters) - The U.S. House of Representatives passed a bill on Tuesday that would give mobile-phone users the right to "unlock" their devices and use them on competitors' wireless networks, although Senate action was uncertain.

The House approved the bill easily, by a 295-114 vote, although some Democrats had pushed back against what they said was a last-minute Republican maneuver to change the legislation.

It is not known whether the Senate will consider the bill.

U.S. wireless carriers often tether, or "lock," smartphones to their networks to encourage consumers to renew their mobile contracts. Consumers, for their part, can often buy new devices at a heavily subsidized price in return for committing to long-term contracts with a single carrier.

Major carriers, including Verizon Wireless, AT&T Inc, Sprint Corp, T-Mobile US and U.S. Cellular, in December made a voluntary pledge to make it easier for consumers to unlock their cellphones, under pressure from consumer groups and the Federal Communications Commission.

Under current law, those unlocking their phones without permission could face legal ramifications, including jail.

The notion of undoing that law has had wide support from Republicans and Democrats since the bill's introduction in the House in 2013.

But the bill's author, Representative Bob Goodlatte, a Virginia Republican, added language after the bill had been approved by a partisan majority of the House Judiciary Committee, banning "bulk unlocking."

Consumer advocates have argued that customers should be allowed to sell their old devices to third parties that could unlock phones in bulk, something the wireless industry opposes.

Four Democrats, led by California Representatives Zoe Lofgren and Anna Eshoo, wrote to their colleagues on Tuesday to protest the bulk unlocking exclusion.

The new provision "could undercut an important court decision that protects consumer choice and prevents monopolistic practices. We cannot in good conscience support a bill that risks giving up so much for so little gain," the Democrats said.

A consumer rights group, Public Knowledge, last week suspended its support of the bill.

(Reporting by Ros Krasny and Alina Selyukh; Editing by Peter Cooney)