The MBTA this week sued Amtrak over the $29 million Amtrak is demanding the authority pay for the right to have Amtrak keep running trains over Northeast Corridor tracks that are owned by the T.

The T warns that if it's forced to make the payments, it might have to take the money out of its already precariously financed mass-transit services.

In its complaint, filed this week in US District Court in Boston, the MBTA says a commission composed largely of representatives of states along the entire Northeast Corridor decided the MBTA had to start paying Amtrak fees for Northeast Corridor service.

This might make sense in other states, where Amtrak owns the tracks and deigns to let commuter-rail trains use them, but in Massachusetts, the T has owned the Northeast Corridor right of way since buying it from Penn Central in 1973.

The T says it has a longstanding contract with Amtrak in which Amtrak gets to use T-owned tracks along the Northeast Corridor between Boston and Rhode Island at no charge - in exchange for the right to dispatch all trains on the line to speed its Acela train to and from points south.

Only Massachusetts and New York representatives on the commission voted against the proposal, which would save some states, including New York, money, while costing others, notably Massachusetts and New Jersey, millions of dollars a year, the MBTA says.

The T charges the new payment system represents a breach of contract:

Amtrak has repudiated the Attleboro Line Agreement. MBTA does not accept that repudiation. MBTA is entitled to a declaration that Amtrak is in breach of the Attleboro Line

Agreement. MBTA also is entitled to an injunction requiring Amtrak to fulfill its obligations under that Agreement because an action for damages would provide an inadequate remedy for breach. Amtrak’s demand for significant, unanticipated payments could have adverse effects on the cost and/or quality of the services that MBTA provides its customers, resulting in a loss of

goodwill among MBTA’s customers and political constituents that cannot readily be calculated.

The T also makes several constitutional arguments against the new system, among them that the Northeast Corridor Infrastructure and Operations Advisory Commission cannot impose such a compact because most of its board is appointed by governors and Amtrak itself, rather than the federal government, which violates the separation of powers and a clause that requires officials taking executive action to be appointed by the president.

Also, the T continues, the new policy violates the authority's right to due process because commission members from states that will save money were not disinterested parties in approving the new system - and neither were the four Amtrak appointees.

Part of the $29-million fee would fund capital projects the T would have no say in, the authority charges, questioning the fairness of making Massachusetts make up capital holes that Congress failed to fill.