On any given day, a teacher's mailbox is usually chock full of messages: leaflets advertising professional development, discount coupons for office supplies, publications from curriculum companies, and book club invitations.

But under a contract that teachers are expected to vote on Thursday, they fear that such communication would cease — unless it comes from the Baltimore Teachers Union.

City teachers are criticizing an unusual clause included in the proposed contract that appears to give the union the exclusive right to disseminate information via email or through teachers' mailboxes. They say the new language is too broad and attempts to silence dissenters and disempower those who organize outside of union parameters.

"The limitation of communication is really disturbing," said Kris Sieloff, a teacher at City Neighbors High School who called the clause a clear First Amendment violation.

The new clause states that "individuals and organizations other than the union shall not be permitted to use the school system's interdepartmental mail and email facilities, or the right of distribution of materials to teachers' mailboxes."

Mike Pesa, a Patterson High School teacher, called the communication clause "nothing less than a gag rule designed to silence any opposition from rank-and-file members of the union."

Marietta English, president of the Baltimore Teachers Union, said the clause was intended to ensure that the union's messages were reaching teachers, and she denied that the clause was intended to muzzle teachers. She said teachers have more than enough ways of communicating.

"Today, it isn't even relevant because everybody tweets and blogs," English said. "More people blog and Facebook more than anything. If you want to communicate, you can communicate. I don't see how we can stop you, when you have every means of communicating today."

But Sieloff, who has taught in Baltimore for a decade, said she was concerned about how teachers would be able to get the word out about forums and other discussions that teachers like to attend to discuss topics in education.

"Teachers want more access to things like that," she said. "It doesn't happen unless you get the word out."

The union announced the new tentative agreement with the district last week after months of negotiations, praising it as a good deal that builds on the successes of the previous contract and preserves benefits that teachers in other districts nationwide are sacrificing.

The three-year pact calls for teachers to receive this month a stipend equal to 1 percent of their annual salary if the contract is ratified, and a 1 percent raise every year through 2016. The contract also calls for teachers' health insurance to stay intact.

The contract maintains key elements of the agreement ratified three years ago, which overhauled the district's pay structure. Traditional "step increases," or automatic annual pay raises, were replaced with a pay-for-performance career ladder that teachers could climb with good evaluations and "achievement units," earned by attending professional development, taking courses or other activities.

"We think this is a good contract," English said. "Last time, this was a whole new contract. We've lived with this now, we've ironed out a lot of the kinks that we had before."

But some city teachers have complaints in addition to objections over the communication clause. Many called the ratification process a rush job designed to suppress debate.

Corey Gaber, a teacher at Southwest Baltimore Charter School, said he took issue with the "fundamentally undemocratic process" of having teachers scrutinize and vote on the contract in a week.

"If you value what your members think about something, then you give them an opportunity to consider the new contract, provide feedback, make changes if necessary, and then vote on it," he said. "This timeline excludes such possibilities, meaning our concerns are not only not being represented by our representatives, there's not even a genuine attempt to listen to them."

English said the vote needed to take place quickly because the contract expired and was extended through Friday.

Teachers also said the contract fails to address long-standing issues with teacher evaluations and working conditions. And some teachers said that while they are happy to keep their benefits, the 1 percent pay increase fails to keep up with the cost of living.

Bobbi O'Brien, a teacher at Patterson High School, said she believed the contract was "unfair."