The United Nations Security Council’s reluctance to sanction Iran over its ballistic missile program is drawing an angry response from a key member of Congress.

Reuters reported Wednesday that U.N. Security Council diplomats don’t think the case for sanctions is very strong because under the relevant U.N. resolution Iran is only “called upon” to not conduct ballistic missile tests that could deliver a nuclear weapon – it is not forbidden from doing so. Even the United States and its allies stopped short of calling the missile tests a “violation” of the resolution in an otherwise strongly-worded letter sent to U.N. officials, according to Reuters.

That “directly contradicts assurances made by the administration,” Senate Foreign Relations Committee Chairman Bob Corker (R-Tenn.) said in a statement Wednesday. “As many of us feared, now it appears Iran can defy those restrictions with impunity, fearing no pushback from the U.N. Security Council.”

Corker, like all Senate Republicans, opposed the Iran nuclear pact, which the U.N. Security Council approved in July by adopting U.N. Security Council Resolution 2231, which also called on Iran not to launch nuclear-capable ballistic missiles. Since the deal was struck, Obama administration officials have insisted that the only sanctions that would be rolled back under the deal are those pertaining to Iran’s nuclear activity — all others would remain in place.

Prior to the Iran deal’s conclusion, the case might have been easier to make. One of the U.N. Security Council resolutions that Resolution 2231 replaced said plainly that Iran “shall not” launch or otherwise conduct activities with ballistic missiles capable of delivering a nuclear warhead.

The Treasury Department has taken steps to sanction Iran over the reported ballistic missile tests, blacklisting individuals and companies that it determined are working to support Iran’s ballistic missile program. There is strong bipartisan support for coming down hard on Iran for the missile tests as well, with several Democrats who supported the Iran deal arguing it is essential to the integrity of that deal to make sure Iran is held to account for its actions elsewhere.

Sens. Corker and Ben Cardin (D-Md.), are expected to soon release legislation stepping up sanctions against Iran over its ballistic missile program.

But the United States and its partners cannot force the U.N. Security Council to take similar actions — and reports that the international community may not follow the United States’ lead with anything more than a public rebuke have Corker crying foul, while other lawmakers are expressing concern.

“US & allies must respond w/ action,” Rep. Ted Deutch (D-Fla.) posted on Twitter Wednesday, citing the same Reuters report. Deutch was one of a small number of Democrats who opposed the Iran deal.